JP3672212B2

JP3672212B2 - Synthetic aperture radar equipment

Info

Publication number: JP3672212B2
Application number: JP29199797A
Authority: JP
Inventors: 雅史岩本; 貴彦藤坂
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1997-10-24
Filing date: 1997-10-24
Publication date: 2005-07-20
Anticipated expiration: 2017-10-24
Also published as: JPH11125674A

Description

【０００１】
【発明の属する技術分野】
この発明は航空機や衛星に搭載する合成開口レーダ装置に係り、地表等を観測して、その３次元地形を測定する装置に関するものである。
【０００２】
【従来の技術】
従来、この種の合成開口レーダ装置としては、図１７に示すようなものがあった。図１７は特開平７−７２２４４号公報に掲載された構成図で、１、２は送受信アンテナ、４、５は送受信部、６は画像処理部、７は干渉処理部、８は地形変動解析処理部、１１は観測する地表などの観測領域である。
また、図１８はこの装置による観測のジオメトリを示したものである。
【０００３】
次に動作について説明する。送受信アンテナ１は送受信部４で発生した高周波パルス信号を観測領域１１へ向けて照射し、その反射波を受信する。また、送受信アンテナ２は送受信部５で発生した高周波パルス信号を観測領域１１へ向けて照射し、その反射波を受信する。二つのアンテナは図１８に示すように、地上の同じ領域を照射するようにビームの角度を調節されているものとする。
【０００４】
画像処理部６はそれぞれのアンテナで受信した信号から観測領域の高分解能レーダ画像を再生する。通常、この種のレーダでは、送信パルスは距離分解能を改善するためにリニアFM変調して帯域幅を拡張しており、周波数対遅延時間特性が送信側と対になる分散型遅延線を利用して分解能の高いパルス波形を復元する。また、プラットフォームの移動に伴い発生するドップラー周波数の時間変化を利用して、これと共役なリファレンス関数とのマッチドフィルタによりアジマス分解能を改善する。このように合成開口レーダの画像再生処理として良く知られた分解能向上の処理により高分解能レーダ画像が得られる。
【０００５】
干渉処理部７は画像処理部６で得られた２枚の複素ＳＡＲ画像の位相差を求める。さらに、送受信アンテナ１と２、および高低差のない理想的な地球ジオイド面における観測領域１１上の任意の点の位置関係から決まる位相変化を取り除くと、等高線に相当する等位相線を求めることができる。この操作は合成開口レーダのインターフェロメトリ処理として知られており、位相差φと地形の高さｈの間の次の関係式を利用して、等位相線から３次元地形を知る方法である。但し、Ｂは送受信アンテナ１と２の間隔、すなわちベースラインの長さ、λは波長、ｒはアンテナと観測領域の距離、θはオフナディア角、αはベースラインの水平面からの傾きである。
【０００６】
【数１】

【０００７】
さらに、地形変動解析処理部８は、過去に観測した３次元地形をデータベース１０に記憶し、標高差算出部９が新たに観測した３次元地形との差を求めるので、２回の観測の間の地形変動を求めることができる。
【０００８】
【発明が解決しようとする課題】
従来の合成開口レーダ装置はこのように構成されているので、移動プラットフォーム上に２台の送受信アンテナを搭載する必要があって、構成が複雑になって重量も増加する問題があった。
【０００９】
また、式（１）からわかるように、地形の高さの精度はプラットフォームと観測領域の距離に反比例して、ベースライン長に比例する。したがって衛星のように遠い軌道から観測する場合には、搭載した２台のアンテナではベースライン長が不足して地形高さの要求精度を満足できない場合が多い。あるいは、ほとんどの衛星はアンテナを１台しか搭載していないので、１回の観測で１枚の画像しか得ることができない。
そこで従来は、衛星が地球を周回して、再び近接した軌道に回帰してくるのを待って、２枚目の画像を観測するRepeat Pass Interferometory の手法がとられている。しかし、この場合には２回の観測の間に数日から数十日の間隔が空くので、観測結果を得るまでの時間遅れが大きいという問題があった。あるいはまた、その間の地表面の変化によって２枚の画像の相関が低下して、高さの誤差が増大するという問題があった。
【００１０】
あるいはまた、限られた送信電力のもとで信号のＳ／Ｎ（Signal to Noise ratio ）を一定値以上に保つためにはアンテナ利得を稼ぐためにビーム幅を狭くせざるを得ず、このため、観測領域が狭い範囲に制限されるという問題があった。
【００１１】
この発明は上記のような問題点を解消するためになされたもので、１台の受信アンテナで、インターフェロメトリ処理に必要な２枚の合成開口レーダ画像を同時に観測できる合成開口レーダ装置を得ることを目的とする。
【００１２】
また、衛星が再び回帰してくるのを待つことなく、一度の観測で３次元地形を得ることのできる合成開口レーダ装置を得ることを目的とする。
【００１３】
あるいはまた、一度の観測で広い範囲の高分解能レーダ画像を得ることのできる合成開口レーダ装置を得ることを目的とする。
【００１４】
【課題を解決するための手段】
この発明の請求項１に係る合成開口レーダ装置は、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置において、観測領域へ高周波パルスを送信する第１の送信アンテナと受信局へそのリファレンス信号を送信する第２の送信アンテナを有し、少なくとも２つの送信局のそれぞれの第１の送信アンテナが所定のベースライン長の隔たりで配置されるように地上に設置された複数の送信局と、観測領域から反射された上記複数の送信局からの高周波パルスを同時に受信する第１の受信アンテナと上記複数の送信局からのリファレンス信号を同時に受信する第２の受信アンテナと、上記第１の受信アンテナと第２の受信アンテナからの一連のパルス列を送信局ごとに分離するパルス弁別手段と、第２の受信アンテナで受信したそれぞれの送信局からのリファレンス信号に同期して第１の受信アンテナで受信した受信信号を復調する復調器とを少なくとも有し、移動プラットフォームに設置された受信局とを備え、上記復調器の出力に基づいて画像処理部で高分解能レーダ画像を求め、得られた少なくとも２枚の合成開口レーダ画像の位相差から干渉処理部で地形の高さを求めるインターフェロメトリ処理により、１回の観測で３次元地形図を得ることを特徴とするものである。
【００１６】
また、この発明の請求項２に係る合成開口レーダ装置は、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置において、観測領域へ高周波パルスを送信する第１の送信アンテナと受信局へそのリファレンス信号を送信する第２の送信アンテナを有し、少なくとも２つの送信局のそれぞれの第１の送信アンテナが所定のベースライン長の隔たりで配置されるように地上に設置された複数の送信局と、上記複数の送信局からの観測領域への高周波パルスの送信のタイミングを観測領域からの反射が互いに干渉しないように制御する送信同期手段と、観測領域から反射された上記複数の送信局からの高周波パルスを受信する第１の受信アンテナと上記複数の送信局からのリファレンス信号を受信する第２の受信アンテナと、第２の受信アンテナで受信したそれぞれの送信局からのリファレンス信号に同期して第１の受信アンテナで受信した受信信号を復調する復調器とを少なくとも有し、移動プラットフォームに設置された受信局とを備え、上記復調器の出力に基づいて画像処理部で高分解能レーダ画像を求め、得られた少なくとも２枚の合成開口レーダ画像の位相差から干渉処理部で地形の高さを求めるインターフェロメトリ処理により、１回の観測で３次元地形図を得ることを特徴とするものである。
【００１７】
また、この発明の請求項３に係る合成開口レーダ装置は、請求項１又は２記載の合成開口レーダ装置において、観測領域に対する送信局と受信局の幾何学的な位置関係に基づいて、所定のレンジ分解能を得られる送信帯域幅を算出し、送信局の送信帯域幅を設定する帯域幅算出手段を備えたことを特徴とするものである。
【００１８】
また、この発明の請求項４に係る合成開口レーダ装置は、請求項１から３のいずれかに記載の合成開口レーダ装置において、送信局と受信局と観測領域の幾何学的な位置関係の変化に応じて、観測領域を見通せる送信局を選出し、選出した送信局の観測領域への入射電力を算出して上記入射電力が大きな送信局を優先的に選択して送信するよう送信局を切り替える送信局選択手段を備えたことを特徴とするものである。
【００１９】
また、この発明の請求項５に係る合成開口レーダ装置は、請求項１記載の合成開口レーダ装置において、送信局と受信局と観測領域の幾何学的な位置関係が適当な２つの送信局について、その一方の送信局の第１の送信アンテナに代えて複数の第１の送信アンテナと上記複数の第１の送信アンテナから１つを選択して使用するように切り替える送信アンテナ選択手段とを備え、観測領域から見た場合の上記２つの送信局の第１の送信アンテナの鉛直方向の見込み角が大きくなるように上記一方の送信局の複数の第１の送信アンテナから１つを選択して使用することを特徴とするものである。
【００２０】
また、この発明の請求項６に係る合成開口レーダ装置は、請求項１記載の合成開口レーダ装置において、送信局と受信局と観測領域の幾何学的な位置関係が適当な１つの送信局について、その送信局の第１の送信アンテナに代えて複数の第１の送信アンテナと上記複数の第１の送信アンテナから１つを選択して使用するように切り替える第１の送信アンテナ選択手段と上記複数の第１の送信アンテナの他に設けた第１の送信アンテナとこの第１の送信アンテナと上記複数の第１の送信アンテナとを切り替える第２の送信アンテナ選択手段とを備え、観測領域から見た場合の上記複数の第１の送信アンテナの他に設けた第１の送信アンテナと上記複数の第１の送信アンテナの１つの第１の送信アンテナの鉛直方向の見込み角が大きくなるように上記複数の第１の送信アンテナから１つを選択して使用することを特徴とするものである。
また、この発明の請求項７に係る合成開口レーダ装置は、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置であって、観測領域へ高周波パルスを送信する第１の送信アンテナと受信局へそのリファレンス信号を送信する第２の送信アンテナを有し、地上に設置された送信局と、観測領域から反射された上記送信局からの高周波パルスを受信する第１の受信アンテナと上記送信局からのリファレンス信号を受信する第２の受信アンテナと、第２の受信アンテナで受信した送信局からのリファレンス信号に同期して第１の受信アンテナで受信した受信信号を復調する復調器とを少なくとも有し、少なくとも２つの受信局のそれぞれの第１の受信アンテナが所定のベースライン長の隔たりで配置されるようにそれぞれ異なる移動プラットフォームに設置された複数の受信局とを備え、上記復調器の出力に基づいて画像処理部で高分解能レーダ画像を求め、少なくとも２つの受信局で得られた２枚の合成開口レーダ画像の位相差から干渉処理部で地形の高さを求めるインターフェロメトリ処理により、１回の観測で３次元地形図を得る合成開口レーダ装置において、送信局と受信局と観測領域の幾何学的な位置関係が適当な１つの送信局について、その送信局の第１の送信アンテナに代えて複数の第１の送信アンテナと上記複数の第１の送信アンテナから１つを選択して使用するように切り替える第１の送信アンテナ選択手段と上記複数の第１の送信アンテナの他に設けた第１の送信アンテナとこの第１の送信アンテナと上記複数の第１の送信アンテナとを切り替える第２の送信アンテナ選択手段とを備え、観測領域から見た場合の上記複数の第１の送信アンテナの他に設けた第１の送信アンテナと上記複数の第１の送信アンテナの１つの第１の送信アンテナの鉛直方向の見込み角が大きくなるように上記複数の第１の送信アンテナから１つを選択して使用することを特徴とするものである。
【００２１】
また、この発明の請求項８に係る合成開口レーダ装置は、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置において、観測領域へ高周波パルスを送信する第１の送信アンテナと受信局へそのリファレンス信号を送信する第２の送信アンテナを有し、複数の観測領域のそれぞれへ高周波パルスを送信する複数の対をなす送信局と、上記それぞれの観測領域から反射された上記複数の対をなす送信局からの高周波パルスを同時に受信する複数の素子アンテナからなるディジタルビームフォーミングアンテナ（ＤＢＦアンテナと称す）と上記複数の対をなす送信局からのリファレンス信号を同時に受信する第２の受信アンテナと、上記ＤＢＦアンテナの出力が入力され、ビームステアリング操作で受信ビームを形成するビーム形成手段と、上記ＤＢＦアンテナと第２の受信アンテナからの一連のパルス列を送信局ごとに分離するパルス弁別手段と、第２の受信アンテナで受信したそれぞれの送信局からのリファレンス信号に同期してＤＢＦアンテナで受信した受信信号を復調する復調器とを少なくとも有する受信局を備え、上記複数の異なる観測領域を同時観測し、上記復調器の出力に基づいて画像処理部で高分解能レーダ画像を求め、得られた少なくとも２枚の合成開口レーダ画像の位相差から干渉処理部で地形の高さを求めるインターフェロメトリ処理により、１回の観測で３次元地形図を得ることを特徴とするものである。
【００２２】
【発明の実施の形態】
実施の形態１．
以下、この発明の実施の形態１の合成開口レーダ装置による観測ジオメトリを図１について説明する。図１において、１２は送信アンテナ、１３は受信アンテナ、１４はリファレンス信号の送信アンテナ、１５はリファレンス信号の受信アンテナ、１６は送信局、１７は受信局である。この実施の形態では、２つの送信局は地上にベースライン長Ｂの間隔をあけて固定されており、受信局１７は航空機などの移動プラットフォームに搭載されているものとする。
【００２３】
この送信局１６の構成を図２に、受信局１７の構成を図３にそれぞれ示す。図２において、１２は送信アンテナ、１４はリファレンス信号の送信アンテナ、１６は送信局、１８は送信部である。図３において、１３は受信アンテナ、１５はリファレンス信号の受信アンテナ、１７は受信局である。また、１９は受信部、２０はパルス弁別手段、２１は復調器である。なお、６と７は図１７のものと同一または同等の手段である。
【００２４】
次に動作について説明する。送信部１８で発生した高周波パルスは、送信アンテナ１２から観測領域１１へ照射される。また、送信信号の一部はリファレンス信号として送信アンテナ１４から受信局１７へ放射される。観測領域１１で反射した信号は受信アンテナ１３で受信され、受信部１９で増幅される。パルス弁別手段２０は、受信信号が、送信局１６ａから送信されたものであるのか、送信局１６ｂで送信されたものであるのか弁別する。そのためには、各パルスに識別用の符号を付加してもよいし、異なる変調をかけておいても良いし、あるいは、あらかじめ送信時刻を決めておいても良い。
【００２５】
それぞれの送信局１６ａ、１６ｂの送信アンテナ１４ａ、１４ｂから送信されたリファレンス信号は受信アンテナ１５で受信されて、受信アンテナ１３での受信信号と同様にパルス弁別手段２０で弁別される。復調器２１は、それぞれの送信局１６ａ、１６ｂからの受信信号とリファレンス信号を組み合わせて復調、検波する。このように送信局１６と受信局１７が分離されたレーダ装置はマルチスタティック方式と呼ばれている。この実施の形態の復調器２１も、これら公知の技術を利用して実現される。
【００２６】
さらに、画像処理部６が、検波された受信信号から高分解能レーダ画像を再生し、干渉処理部７が２枚の高分解能レーダ画像の位相差から３次元地形を算出する。その動作は従来例における画像処理部６、干渉処理部７と同様である。
【００２７】
このように本実施の形態の構成によれば、異なる位置に配置された複数の送信局１６が高周波パルス信号を送信し、移動プラットフォームに搭載された受信局１７が地上で反射した信号を受信して、パルス弁別手段２０がそれぞれの送信局からの受信信号あるいはリファレンス信号を弁別するので、送信局と受信局の幾何学的位置関係の異なる条件で観測された高分解能レーダ画像を同時に得ることができて、１回の観測で３次元地形図を得ることができる。
また、送信局を地上や大型航空機に設置した場合には、大きな送信電力を実現することができるので、Ｓ／Ｎ（Signal to Noise ratio）の良い高分解能レーダ画像を得ることができる。
【００２８】
なお、画像処理部６と干渉処理部７は必ずしも移動プラットフォーム上に搭載する必要はなく、地上などに分離して設置してもかまわず、受信局を軽量化できる。
また、送信局と受信局が地上、航空機あるいは衛星などの移動プラットフォームに分離して設けられていれば良く、受信局の代わりに送信局が移動プラットフォームに搭載されていてもかまわない。
【００２９】
実施の形態２．
以下、この発明の実施の形態２の合成開口レーダ装置の観測ジオメトリを図４について説明する。図４において、１２〜１７は図１のものと同一または同等のものである。この実施の形態では、送信局１６は地上に固定されており、複数の受信局１７は航空機などの異なる移動プラットフォームにそれぞれ搭載されているものとする。
【００３０】
この送信局１６の構成を図５に、受信局１７の構成を図６にそれぞれ示す。これらの図において６〜２１は図２、３のものと同一または同等のものである。
【００３１】
次に動作について説明する。この実施の形態の装置の動作は実施の形態１で説明した装置の動作とほぼ同じであり、送信局１６と受信局１７の動作は図２および図３に示した送信局と受信局の動作と概ね同様である。但し、この実施の形態では送信局が１局だけなので、受信局でパルスを弁別する必要がなく、このため実施の形態１に比べて受信局の構成を簡単にできる。
【００３２】
このようにこの実施の形態の構成によれば、送信局１６が高周波パルス信号を送信し、複数の移動プラットフォームにそれぞれ搭載された受信局１７が観測領域で反射した信号を受信するので、１回の観測で送信局１６と受信局１７の幾何学的位置関係の異なる条件で観測された高分解能レーダ画像を同時に得ることができて、３次元地形図を得ることができる。
なお、ここでは通常、干渉処理部７は移動プラットフォーム上に搭載せず、地上などに分離して設置し、複数の受信局１７から信号を受けて処理を行なう。
【００３３】
実施の形態３．
以下、この発明の実施の形態３の合成開口レーダ装置を図７について説明する。図７はこの装置の送信局１６の構成を説明する図で、図において、１１〜１８は図２のものと同一または同等のものである。２２は複数の送信局間の送信のタイミングを制御する送信同期手段である。また、この装置の観測ジオメトリと受信局は実施の形態１で示した図１、図３と同様である。
【００３４】
次に動作について説明する。図７において送信部１８と送信アンテナ１２、リファレンス信号の送信アンテナ１４の動作は実施の形態１の装置と同様である。送信同期手段２２は、複数の送信局が同時に送信することがないように、あるいは、複数の送信局からの信号が同時に受信局に到達しないように、それぞれの送信局が送信する時間を制御する。例えば、複数の送信局に、あらかじめ決められた時間間隔で、順番に送信許可を与える。
【００３５】
このように本実施の形態の構成によれば、信号が混信して無駄になることなくすべて有効に利用することができる。あるいは、送信パルスに識別用の符号を付加したり、識別用の変調をかけることなく実施の形態１と同様の効果を得ることができる。
【００３６】
実施の形態４．
以下、この発明の実施の形態４の合成開口レーダ装置を図８について説明する。図８はこの装置の送信局の構成を説明する図で、図において、１１〜１８は図２のものと同一または同等のものである。２３は帯域幅算出手段である。また、この装置の観測ジオメトリを図９に示す。なお、この装置の受信局は実施の形態１の装置と同様である。
【００３７】
次に動作について説明する。図８において、送信部１８と送信アンテナ１２、リファレンス信号の送信アンテナ１４の動作は実施の形態１の装置と同様である。帯域幅算出手段２３は、画像のレンジ分解能が要求値と一致するように、それぞれの送信局１６ａ、１６ｂの送信帯域幅を算出して制御する。
【００３８】
送信局と受信局が同じ位置にある、いわゆるモノスタティックレーダの場合、送信帯域幅Ｂとレンジ分解能Δｒの間には次の関係があることはよく知られている。但し、Ｃは電波伝播速度である。また、θは観測領域において地表の垂線と電波の入射角度とがなす角度で、電波入射角と呼ばれる。
【００３９】
【数２】

【００４０】
一方、この実施の形態のように、送信局１６と受信局１７が異なる位置にある、いわゆるマルチスタティック方式の場合、送信帯域幅Ｂとレンジ分解能Δｒの間には次の関係が成立する。但し、θ₁ 、θ₂ は、それぞれ送信局側と受信局側の電波入射角で、図９に示す角度である。
【００４１】
【数３】

【００４２】
すなわち、マルチスタティックレーダでレンジ分解能を所期の値にするためには、送信局と受信局と観測領域の位置関係に応じて送信帯域幅を変える必要がある。
【００４３】
従って、この実施の形態の構成によれば、帯域幅算出手段２３を備え、送信局と受信局と観測領域の位置関係に応じて送信帯域幅を変えるので、送信局と受信局と観測領域の位置関係に依らず所望のレンジ分解能の高分解能レーダ画像を得ることができる。
【００４４】
実施の形態５．
以下、この発明の実施の形態５の合成開口レーダ装置を図１０について説明する。図１０はこの装置の送信局の構成を説明する図で、図において、１１〜１８は図２のものと同一または同等のものである。２４は送信局選択手段である。また、この装置の観測ジオメトリと受信局は実施の形態１の装置と同様である。
【００４５】
次に動作について説明する。図１０において送信部１８と送信アンテナ１２、リファレンス信号の送信アンテナ１４の動作は実施の形態１の装置と同様である。送信局選択手段２４は、複数の送信局と受信局と観測領域の幾何学的な位置関係を考慮して、送信を行う送信局を選択する。送信局の選択手順は例えば次のように表わされる。
【００４６】
（ＳＴ０１）
観測領域を見通せる送信局を選抜する。
【００４７】
（ＳＴ０２）
次式に従ってそれぞれの送信局毎に観測領域の単位面積あたりの入射電力を計算して、これが大きな送信局を優先的に選択する。但し、Ｐ_t は送信電力、Ｇ_t は送信アンテナの利得、Ｒは送信局と観測領域の距離、θ₁ は観測領域における電波入射角である。これらの観測ジオメトリを図１１に示す。
【００４８】
【数４】

【００４９】
このようにこの実施の形態の構成によれば、観測領域への単位面積当たりの入射電力が大きな送信局を優先的に選択することができるので、Ｓ／Ｎの優れた高分解能レーダ画像を得ることができる。
【００５０】
実施の形態６．
以下、この発明の実施の形態６の合成開口レーダ装置を図１２について説明する。この実施の形態６では、予め既知の複数の送信局と受信局と観測領域の位置関係から、送信局と受信局と観測領域の幾何学的な位置関係が適当な２つの送信局を選定しておき、その一方の送信局を図１２に示すような構成のものにするものである。図１２はこの装置の送信局の構成を説明する図で、図において、１１〜１８は図２のものと同一または同等のものである。２５は送信アンテナ選択手段である。また、この装置の観測ジオメトリを図１３に示す。なお、この装置の受信局の構成は実施の形態１の装置と同様である。
【００５１】
次に動作について説明する。図１２において送信部１８と送信アンテナ１２、リファレンス信号の送信アンテナ１４の動作は実施の形態１の装置と同様である。送信アンテナ選択手段２５は、複数の送信アンテナと受信局と観測領域の幾何学的な位置関係を考慮して、電波を放射する送信アンテナを選択する。
【００５２】
これは、インターフェロメトリ処理を行う場合には、いわゆる光学のステレオ視の場合と同様に、分離したい方向（この場合は鉛直方向）の見込み角が大きな位置から観測した結果を組み合わせる場合に最も感度を高くすることができるためである。
【００５３】
従って、送信アンテナ選択手段２５による送信アンテナの選択は例えば次のように行う。
観測領域から見て、一方の送信局１６ａの複数の送信アンテナ１２ｃ〜１２ｅから、選定した２つの送信局１６ａ、１６ｂの送信アンテナの方位方向の見込み角が小さくて、かつ鉛直方向の見込み角が大きくなる送信アンテナを選択する。例えば、（鉛直方向の見込み角−方位方向の見込み角）が最大になる送信アンテナを選択する。
【００５４】
このようにこの実施の形態の構成によれば、観測領域からの鉛直方向の見込み角の大きな送信アンテナの組み合わせを優先的に選択することができるので、高さの精度の優れた３次元地形図を得ることができる。
【００５５】
実施の形態７．
以下、この発明の実施の形態７の合成開口レーダ装置を図１４について説明する。図１４はこの装置の送信局の構成を説明する図で、図において、１１〜１８と２５は図１２のものと同一または同等のものである。また、この装置の観測ジオメトリは実施の形態６の図１３と同様であり、受信局の構成は図３と同様である。
【００５６】
次に動作について説明する。この実施の形態７の装置は、１つの送信局のみで実施の形態６と同様の効果を得るものである。図１４において、送信部１８と送信アンテナ１２、リファレンス信号の送信アンテナ１４、送信アンテナ選択手段２５ａの動作は実施の形態６の装置と同様である。送信アンテナ選択手段２５ｂは送信アンテナ１２ｂと送信アンテナ群１２ｃ〜１２ｅがあたかも異なる送信局であるかのように、切り替え動作する。
【００５７】
このようにこの実施の形態の構成によれば、１つの送信局で送信アンテナ選択手段２５ｂの切り替え動作により、インターフェロメトリ処理に必要な２枚の画像を得ることができ、しかも送信アンテナ選択手段２５ａで観測領域からの鉛直方向の見込み角の大きな送信アンテナの組み合わせを優先的に選択することができるので、１つの送信局で高さの精度の優れた３次元地形図を得ることができる。
【００５８】
実施の形態８．
以下、この発明の実施の形態８の合成開口レーダ装置を図１５について説明する。この実施の形態８は複数の異なる観測領域を同時観測し、１回の観測で複数の観測領域の３次元地形図を得るものである。図１５はこの装置の受信局の構成を説明する図で、図において
、１１と１５〜２１は図３のものと同一または同等のものである。１３は複数の素子アンテナからなるＤＢＦアンテナである受信アンテナ、２６はビーム形成手段である。また、この装置の観測ジオメトリを図１６に示す。図において、１１〜１７は実施の形態１と同一または同等のものである。なお、それぞれの送信局の構成は実施の形態２の装置と同様である。
【００５９】
次に動作について説明する。受信アンテナ１３はＤＢＦアンテナであり、それぞれの素子アンテナの出力は受信部１９にて増幅された後、ビーム形成手段２６に入力される。ビーム形成手段２６はよく知られた次式のビームステアリング操作によって、受信ビームを所望の方向へ形成する。但し、Ｓ′は角度ηのビーム出力、ｉはＤＢＦアンテナの素子アンテナ番号、Ｓ_i は第ｉ素子アンテナの出力信号、ｄは素子間隔、λは波長である。なお、ここでは１次元のビーム形成を例示したが、この式は２次元の場合にも容易に拡張することができる。
【００６０】
【数５】

【００６１】
ビームステアリング操作は複数の方向について並列に演算することが可能であり、従ってＤＢＦアンテナで得られた受信信号から複数の受信ビームを同時に形成することができる。それぞれのビームの受信信号はパルス弁別手段２０へ入力されて、以下、実施の形態１での図３の説明同様に動作する。
【００６２】
すなわち図１６に示すように、複数の観測領域から反射してくる信号を１つの受信局で同時に受信して処理することができる。
【００６３】
このように実施の形態８の構成によれば、１回の同時観測で１つの受信局により複数の観測領域の高分解能レーダ画像、および３次元地形図を同時に得ることができる。
【００６４】
【発明の効果】
この発明は、以上説明したように構成されているので、以下に記載されるような効果を奏する。
【００６５】
この発明によれば、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置において、１つの受信局を備えることで１回の観測で３次元地形図を得られる合成開口レーダ装置を実現できる効果がある。
【００６６】
また、送信局と受信局を、地上、航空機あるいは衛星などの移動プラットフォームに分離して設けて構成するマルチスタティック方式の合成開口レーダ装置において、１つの送信局を用いた構成としたので、受信局にパルス弁別手段が不要となり、簡単な構成の受信局で１回の観測で３次元地形図を得られる合成開口レーダ装置を実現できる効果がある。
【００６７】
あるいは、１回の観測で３次元の地形図を得ることができる合成開口レーダ装置を実現することができる。
【００６８】
また、送信局と受信局と観測領域の位置関係によらず１回の観測で所望のレンジ分解能の高分解能レーダ画像を得ることができる効果がある。
【００６９】
また、１回の観測でＳ／Ｎの優れた高分解能レーダ画像を得ることができる効果がある。
【００７０】
また、１回の観測で高さの精度の優れた３次元地形図を得られる効果がある。
【００７１】
また、１つの送信局により高さの精度の優れた３次元地形図を得られる効果がある。
【００７２】
さらに、複数の異なる観測領域を同時観測し、１回の観測で１つの受信局により複数の観測領域の３次元地形図を同時に得ることができる効果がある。
【図面の簡単な説明】
【図１】この発明の実施の形態１の合成開口レーダ装置の観測ジオメトリの説明図である。
【図２】この発明の実施の形態１の合成開口レーダ装置の送信局の構成図である。
【図３】この発明の実施の形態１の合成開口レーダ装置の受信局の構成図である。
【図４】この発明の実施の形態２の合成開口レーダ装置の観測ジオメトリの説明図である。
【図５】この発明の実施の形態２の合成開口レーダ装置の送信局の構成図である。
【図６】この発明の実施の形態２の合成開口レーダ装置の受信局の構成図である。
【図７】この発明の実施の形態３の合成開口レーダ装置の送信局の構成図である。
【図８】この発明の実施の形態４の合成開口レーダ装置の送信局の構成図である。
【図９】この発明の実施の形態４の合成開口レーダ装置の観測ジオメトリの説明図である。
【図１０】この発明の実施の形態５の合成開口レーダ装置の送信局の構成図である。
【図１１】この発明の実施の形態５の合成開口レーダ装置の観測ジオメトリの説明図である。
【図１２】この発明の実施の形態６の合成開口レーダ装置の送信局の構成図である。
【図１３】この発明の実施の形態６の合成開口レーダ装置の観測ジオメトリの説明図である。
【図１４】この発明の実施の形態７の合成開口レーダ装置の送信局の構成図である。
【図１５】この発明の実施の形態８の合成開口レーダ装置の受信局の構成図である。
【図１６】この発明の実施の形態８の合成開口レーダ装置の観測ジオメトリの説明図である。
【図１７】従来の合成開口レーダ装置の構成図である。
【図１８】従来の合成開口レーダ装置の観測ジオメトリの説明図である。
【符号の説明】
１、２送受信アンテナ、３送受信アンテナ群、４、５送受信部、
６画像処理部、７干渉処理部、８地形変動解析処理部、
９標高差検出部、１０データベース、１１観測領域、
１２送信アンテナ、１３受信アンテナ、１４リファレンス信号の送信アンテナ、１５リファレンス信号の受信アンテナ、１６送信局、１７受信局、１８送信部、１９受信部、２０パルス弁別手段、２１復調器、２２送信同期手段、２３帯域幅算出手段、２４送信局選択手段、２５送信アンテナ選択手段、２６ビーム形成手段。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synthetic aperture radar apparatus mounted on an aircraft or a satellite, and relates to an apparatus for observing the ground surface and measuring its three-dimensional topography.
[0002]
[Prior art]
Conventionally, this type of synthetic aperture radar apparatus has been shown in FIG. FIG. 17 is a block diagram published in Japanese Patent Application Laid-Open No. 7-72244. Reference numerals 1 and 2 are transmission / reception antennas, 4 and 5 are transmission / reception units, 6 is an image processing unit, 7 is an interference processing unit, and 8 is terrain variation analysis processing. Reference numeral 11 denotes an observation area such as a ground surface to be observed.
FIG. 18 shows an observation geometry by this apparatus.
[0003]
Next, the operation will be described. The transmission / reception antenna 1 irradiates the observation region 11 with the high-frequency pulse signal generated by the transmission / reception unit 4 and receives the reflected wave. The transmission / reception antenna 2 irradiates a high-frequency pulse signal generated by the transmission / reception unit 5 toward the observation region 11 and receives the reflected wave. As shown in FIG. 18, it is assumed that the angle of the beam is adjusted so that the two antennas irradiate the same area on the ground.
[0004]
The image processing unit 6 reproduces a high-resolution radar image of the observation area from signals received by the respective antennas. Normally, in this type of radar, the transmission pulse is linear FM modulated to improve the distance resolution and the bandwidth is expanded, and a distributed delay line whose frequency vs. delay time characteristic is paired with the transmission side is used. Restore the pulse waveform with high resolution. Also, by utilizing the time change of the Doppler frequency generated with the movement of the platform, the azimuth resolution is improved by a matched filter of this and a conjugate reference function. In this way, a high resolution radar image can be obtained by a resolution improvement process well known as an image reproduction process of a synthetic aperture radar.
[0005]
The interference processing unit 7 obtains the phase difference between the two complex SAR images obtained by the image processing unit 6. Furthermore, isophase lines corresponding to contour lines can be obtained by removing phase changes determined from the positional relationship between the transmitting and receiving antennas 1 and 2 and an arbitrary point on the observation region 11 in an ideal earth geoid plane with no height difference. it can. This operation is known as interferometry processing of synthetic aperture radar, and is a method of knowing a three-dimensional topography from isophase lines using the following relational expression between the phase difference φ and the topography height h. . Where B is the distance between the transmitting and receiving antennas 1 and 2, that is, the length of the baseline, λ is the wavelength, r is the distance between the antenna and the observation area, θ is the off-nadir angle, and α is the inclination of the baseline from the horizontal plane.
[0006]
[Expression 1]

[0007]
Furthermore, the terrain fluctuation analysis processing unit 8 stores the three-dimensional terrain observed in the past in the database 10 and obtains a difference from the newly observed three-dimensional terrain by the altitude difference calculation unit 9. Terrain fluctuations can be obtained.
[0008]
[Problems to be solved by the invention]
Since the conventional synthetic aperture radar apparatus is configured as described above, it is necessary to mount two transmission / reception antennas on the mobile platform, and there is a problem that the configuration becomes complicated and the weight increases.
[0009]
As can be seen from Equation (1), the accuracy of the height of the terrain is inversely proportional to the distance between the platform and the observation area, and proportional to the baseline length. Therefore, when observing from a distant orbit like a satellite, the two installed antennas often do not satisfy the required accuracy of terrain height due to insufficient baseline length. Alternatively, since most satellites have only one antenna, only one image can be obtained in one observation.
Therefore, conventionally, the repeat pass interferometory method is used in which the satellite orbits the earth and waits for it to return to a close orbit again to observe the second image. However, in this case, there is a problem that the time delay until obtaining the observation result is large because there is an interval of several days to several tens of days between the two observations. Alternatively, there is a problem in that the correlation between the two images decreases due to a change in the ground surface between them, and the height error increases.
[0010]
Alternatively, in order to maintain the signal to noise ratio (S / N) of a signal under a limited transmission power at a certain value or more, the beam width must be narrowed in order to increase the antenna gain. There is a problem that the observation area is limited to a narrow range.
[0011]
The present invention has been made to solve the above-described problems, and provides a synthetic aperture radar device capable of simultaneously observing two synthetic aperture radar images necessary for interferometry processing with a single receiving antenna. For the purpose.
[0012]
It is another object of the present invention to provide a synthetic aperture radar apparatus that can obtain a three-dimensional landform with a single observation without waiting for the satellite to return again.
[0013]
Another object is to obtain a synthetic aperture radar apparatus that can obtain a wide range of high-resolution radar images by a single observation.
[0014]
[Means for Solving the Problems]
A synthetic aperture radar apparatus according to claim 1 of the present invention is a multistatic synthetic aperture radar apparatus in which a transmitting station and a receiving station are separately provided on a mobile platform such as the ground, an aircraft, or a satellite. A first transmission antenna that transmits a high-frequency pulse to the second transmission antenna and a second transmission antenna that transmits the reference signal to the reception station. Each of the first transmission antennas of at least two transmission stations has a predetermined baseline length. A plurality of transmitting stations installed on the ground so as to be spaced apart from each other, a first receiving antenna that simultaneously receives high-frequency pulses from the plurality of transmitting stations reflected from the observation region, and the plurality of transmitting stations. A second receiving antenna that receives the reference signal simultaneously, and a series of pulses from the first receiving antenna and the second receiving antenna And at least a demodulator that demodulates the received signal received by the first receiving antenna in synchronization with the reference signal from each transmitting station received by the second receiving antenna. A high-resolution radar image obtained by the image processing unit based on the output of the demodulator, and interfering from the phase difference between the obtained synthetic aperture radar images. A three-dimensional topographic map is obtained by one observation by interferometry processing for obtaining the height of the topography by the processing unit.
[0016]
  Further, the claims of the present invention2The synthetic aperture radar apparatus according to the present invention is a multi-static synthetic aperture radar apparatus in which a transmitting station and a receiving station are separately provided on a mobile platform such as the ground, an aircraft, or a satellite, and transmits high-frequency pulses to an observation region. A first transmitting antenna and a second transmitting antenna for transmitting the reference signal to the receiving station, and the first transmitting antennas of the at least two transmitting stations are arranged with a predetermined baseline length apart A plurality of transmitting stations installed on the ground, transmission synchronization means for controlling the transmission timing of the high-frequency pulse from the plurality of transmitting stations to the observation region so that reflections from the observation region do not interfere with each other, and the observation region A first receiving antenna for receiving high frequency pulses reflected from the plurality of transmitting stations and a reference from the plurality of transmitting stations. At least a second receiving antenna that receives the received signal and a demodulator that demodulates the received signal received by the first receiving antenna in synchronization with the reference signal from each transmitting station received by the second receiving antenna. A high-resolution radar image obtained by the image processing unit based on the output of the demodulator, and interfering from the phase difference between the obtained synthetic aperture radar images. A three-dimensional topographic map is obtained by one observation by interferometry processing for obtaining the height of the topography by the processing unit.
[0017]
  Further, the claims of the present invention3A synthetic aperture radar device according to claim 1 is provided.Or 2In the described synthetic aperture radar device, a transmission bandwidth capable of obtaining a predetermined range resolution is calculated based on a geometric positional relationship between the transmission station and the reception station with respect to the observation region, and the transmission bandwidth of the transmission station is set. A bandwidth calculating means is provided.
[0018]
  Further, the claims of the present invention4A synthetic aperture radar device according to claim 1 is provided.To any of 3In the described synthetic aperture radar device, a transmitting station that can see the observation area is selected according to a change in the geometric positional relationship between the transmission station, the receiving station, and the observation area, and the incident power to the observation area of the selected transmission station is selected. And transmitting station selecting means for switching the transmitting station so as to preferentially select and transmit the transmitting station having a large incident power.
[0019]
  Further, the claims of the present invention5The synthetic aperture radar apparatus according to claim 1 is the synthetic aperture radar apparatus according to claim 1, wherein two transmitting stations having an appropriate geometric positional relationship between the transmitting station, the receiving station, and the observation area are the first transmitting station. A plurality of first transmission antennas instead of one transmission antenna and transmission antenna selection means for switching to use one of the plurality of first transmission antennas, and when viewed from the observation region One selected from a plurality of first transmitting antennas of the one transmitting station so that a vertical angle of the first transmitting antenna of the two transmitting stations is increased. It is.
[0020]
  Further, the claims of the present invention6A synthetic aperture radar device according to claim1In the synthetic aperture radar apparatus described above, a plurality of first transmissions for a single transmission station having an appropriate geometrical positional relationship between the transmission station, the reception station, and the observation area are used instead of the first transmission antenna of the transmission station. A first transmission antenna selecting means for switching to use one of the plurality of antennas and the plurality of first transmission antennas; a first transmission antenna provided in addition to the plurality of first transmission antennas; and A second transmission antenna selecting means for switching between the first transmission antenna and the plurality of first transmission antennas; a first provided in addition to the plurality of first transmission antennas when viewed from the observation region; Selecting one of the plurality of first transmission antennas to be used so that a vertical angle of view of the first transmission antenna of the plurality of first transmission antennas and one first transmission antenna of the plurality of first transmission antennas is increased. Special It is an.
  The synthetic aperture radar apparatus according to claim 7 of the present invention is a multi-static synthetic aperture radar apparatus in which a transmitting station and a receiving station are separately provided on a mobile platform such as the ground, an aircraft, or a satellite. A first transmission antenna that transmits a high-frequency pulse to the observation region and a second transmission antenna that transmits the reference signal to the reception station, the transmission station installed on the ground, and the above-described reflected from the observation region A first receiving antenna that receives a high frequency pulse from the transmitting station, a second receiving antenna that receives a reference signal from the transmitting station, and a reference signal from the transmitting station that is received by the second receiving antenna. And a demodulator that demodulates a received signal received by the first receiving antenna, and each of the first receiving antennas of each of the at least two receiving stations. A plurality of receiving stations installed on different mobile platforms such that tenors are arranged at a predetermined baseline length apart, and a high resolution radar image is obtained by an image processing unit based on the output of the demodulator, Synthetic aperture radar that obtains a three-dimensional topographic map in one observation by interferometry processing that obtains the height of the topography by the interference processing unit from the phase difference between two synthetic aperture radar images obtained by at least two receiving stations In the apparatus, for one transmitting station in which the geometric positional relationship between the transmitting station, the receiving station, and the observation region is appropriate, instead of the first transmitting antenna of the transmitting station, a plurality of first transmitting antennas and the plurality of transmitting stations A first transmission antenna provided in addition to the first transmission antenna selecting means for switching to use one of the first transmission antennas and the plurality of first transmission antennas. And a second transmission antenna selection means for switching between the first transmission antenna and the plurality of first transmission antennas, provided in addition to the plurality of first transmission antennas when viewed from the observation region One of the first transmission antennas and one of the plurality of first transmission antennas are used by selecting one of the plurality of first transmission antennas so that the vertical angle of view of the first transmission antenna is large. It is characterized by this.
[0021]
  A synthetic aperture radar apparatus according to claim 8 of the present invention.SendA first transmission antenna and a receiving station for transmitting a high-frequency pulse to an observation region in a multi-static synthetic aperture radar apparatus in which a transmission station and a receiving station are separately provided on a mobile platform such as the ground, an aircraft, or a satellite. A second transmitting antenna for transmitting a reference signal to the navel, and a plurality of pairs of transmitting stations for transmitting high-frequency pulses to each of a plurality of observation regions; and the plurality of pairs reflected from each of the observation regions. A digital beamforming antenna (referred to as a DBF antenna) comprising a plurality of element antennas that simultaneously receive high-frequency pulses from a transmitting station that constitutes a second receiving antenna that simultaneously receives reference signals from a plurality of pairs of transmitting stations. And the output of the DBF antenna is inputted, and the beam is operated by beam steering operation. Beam forming means for forming, pulse discriminating means for separating a series of pulse trains from the DBF antenna and the second receiving antenna for each transmitting station, and reference signals from the respective transmitting stations received by the second receiving antenna. A reception station having at least a demodulator that demodulates a received signal received by a DBF antenna in synchronization, and simultaneously observes the plurality of different observation areas, and a high-resolution radar in an image processor based on the output of the demodulator A three-dimensional topographic map is obtained by one observation by interferometry processing in which an image is obtained, and the height of the topography is obtained by an interference processing unit from the phase difference between at least two obtained synthetic aperture radar images. To do.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
The observation geometry by the synthetic aperture radar apparatus according to Embodiment 1 of the present invention will be described below with reference to FIG. In FIG. 1, 12 is a transmission antenna, 13 is a reception antenna, 14 is a reference signal transmission antenna, 15 is a reference signal reception antenna, 16 is a transmission station, and 17 is a reception station. In this embodiment, it is assumed that the two transmitting stations are fixed on the ground with an interval of the baseline length B, and the receiving station 17 is mounted on a mobile platform such as an aircraft.
[0023]
The configuration of the transmitting station 16 is shown in FIG. 2, and the configuration of the receiving station 17 is shown in FIG. In FIG. 2, 12 is a transmission antenna, 14 is a reference signal transmission antenna, 16 is a transmission station, and 18 is a transmission unit. In FIG. 3, 13 is a receiving antenna, 15 is a receiving antenna for a reference signal, and 17 is a receiving station. Reference numeral 19 is a receiving unit, 20 is a pulse discriminating means, and 21 is a demodulator. 6 and 7 are the same or equivalent means as in FIG.
[0024]
Next, the operation will be described. The high frequency pulse generated in the transmission unit 18 is irradiated from the transmission antenna 12 to the observation region 11. A part of the transmission signal is radiated from the transmission antenna 14 to the reception station 17 as a reference signal. The signal reflected by the observation region 11 is received by the receiving antenna 13 and amplified by the receiving unit 19. The pulse discriminating means 20 discriminates whether the received signal is transmitted from the transmitting station 16a or transmitted from the transmitting station 16b. For this purpose, an identification code may be added to each pulse, different modulation may be applied, or the transmission time may be determined in advance.
[0025]
The reference signals transmitted from the transmitting

antennas

14a and 14b of the transmitting

stations

16a and 16b are received by the receiving antenna 15 and discriminated by the pulse discriminating means 20 in the same manner as the received signal at the receiving antenna 13. The demodulator 21 demodulates and detects the received signal from each of the

transmission stations

16a and 16b and the reference signal in combination. The radar apparatus in which the transmitting station 16 and the receiving station 17 are separated in this way is called a multistatic system. The demodulator 21 of this embodiment is also realized using these known techniques.
[0026]
Further, the image processing unit 6 reproduces a high resolution radar image from the detected received signal, and the interference processing unit 7 calculates a three-dimensional landform from the phase difference between the two high resolution radar images. The operation is the same as that of the image processing unit 6 and the interference processing unit 7 in the conventional example.
[0027]
As described above, according to the configuration of the present embodiment, a plurality of transmitting stations 16 arranged at different positions transmit high-frequency pulse signals, and a receiving station 17 mounted on a mobile platform receives signals reflected on the ground. Thus, since the pulse discriminating means 20 discriminates the received signal or reference signal from each transmitting station, it is possible to simultaneously obtain high resolution radar images observed under different conditions of the geometric positional relationship between the transmitting station and the receiving station. A three-dimensional topographic map can be obtained with one observation.
Further, when the transmitting station is installed on the ground or a large aircraft, a large transmission power can be realized, so that a high-resolution radar image with a good S / N (Signal to Noise ratio) can be obtained.
[0028]
Note that the image processing unit 6 and the interference processing unit 7 do not necessarily have to be mounted on the mobile platform, and may be separately installed on the ground or the like, thereby reducing the weight of the receiving station.
The transmitting station and the receiving station may be provided separately on a mobile platform such as the ground, an aircraft, or a satellite, and the transmitting station may be mounted on the mobile platform instead of the receiving station.
[0029]
Embodiment 2. FIG.
The observation geometry of the synthetic aperture radar device according to the second embodiment of the present invention will be described below with reference to FIG. 4, 12 to 17 are the same as or equivalent to those in FIG. In this embodiment, it is assumed that the transmitting station 16 is fixed on the ground, and the plurality of receiving stations 17 are mounted on different mobile platforms such as aircraft.
[0030]
The configuration of the transmitting station 16 is shown in FIG. 5, and the configuration of the receiving station 17 is shown in FIG. In these figures, 6 to 21 are the same as or equivalent to those in FIGS.
[0031]
Next, the operation will be described. The operation of the apparatus of this embodiment is almost the same as that of the apparatus described in Embodiment 1, and the operations of the transmitting station 16 and the receiving station 17 are the operations of the transmitting station and the receiving station shown in FIGS. It is almost the same. However, in this embodiment, since there is only one transmitting station, there is no need to discriminate pulses at the receiving station, and therefore the configuration of the receiving station can be simplified compared to the first embodiment.
[0032]
As described above, according to the configuration of this embodiment, the transmitting station 16 transmits the high-frequency pulse signal, and the receiving station 17 mounted on each of the plurality of mobile platforms receives the signal reflected from the observation region. In this observation, a high-resolution radar image observed under different conditions of the geometric positional relationship between the transmitting station 16 and the receiving station 17 can be obtained simultaneously, and a three-dimensional topographic map can be obtained.
Here, normally, the interference processing unit 7 is not mounted on the mobile platform, but is installed separately on the ground or the like, and receives signals from a plurality of receiving stations 17 to perform processing.
[0033]
Embodiment 3 FIG.
A synthetic aperture radar apparatus according to Embodiment 3 of the present invention will be described below with reference to FIG. FIG. 7 is a diagram for explaining the configuration of the transmission station 16 of this apparatus. In the figure, reference numerals 11 to 18 are the same as or equivalent to those in FIG. Reference numeral 22 denotes transmission synchronization means for controlling transmission timing between a plurality of transmission stations. The observation geometry and receiving station of this apparatus are the same as those shown in FIGS. 1 and 3 described in the first embodiment.
[0034]
Next, the operation will be described. In FIG. 7, the operations of the transmission unit 18, the transmission antenna 12, and the reference signal transmission antenna 14 are the same as those of the apparatus of the first embodiment. The transmission synchronization means 22 controls the transmission time of each transmitting station so that a plurality of transmitting stations do not transmit at the same time or signals from a plurality of transmitting stations do not reach the receiving station at the same time. . For example, transmission permission is given to a plurality of transmitting stations in order at predetermined time intervals.
[0035]
As described above, according to the configuration of the present embodiment, all signals can be effectively used without being mixed and wasted. Alternatively, the same effect as in the first embodiment can be obtained without adding an identification code to the transmission pulse or applying modulation for identification.
[0036]
Embodiment 4 FIG.
A synthetic aperture radar apparatus according to Embodiment 4 of the present invention will be described below with reference to FIG. FIG. 8 is a diagram for explaining the configuration of the transmitting station of this apparatus. In the figure, reference numerals 11 to 18 are the same as or equivalent to those in FIG. Reference numeral 23 denotes a bandwidth calculation means. Moreover, the observation geometry of this apparatus is shown in FIG. The receiving station of this apparatus is the same as that of the apparatus of the first embodiment.
[0037]
Next, the operation will be described. In FIG. 8, the operations of the transmission unit 18, the transmission antenna 12, and the reference signal transmission antenna 14 are the same as those of the apparatus of the first embodiment. The bandwidth calculation unit 23 calculates and controls the transmission bandwidth of each of the

transmission stations

16a and 16b so that the range resolution of the image matches the required value.
[0038]
In the case of a so-called monostatic radar in which the transmitting station and the receiving station are at the same position, it is well known that the following relationship exists between the transmission bandwidth B and the range resolution Δr. Where C is the radio wave propagation speed. In addition, θ is an angle formed by a vertical line on the ground surface and an incident angle of a radio wave in an observation region, and is called a radio wave incident angle.
[0039]
[Expression 2]

[0040]
On the other hand, in the case of a so-called multistatic system in which the transmitting station 16 and the receiving station 17 are at different positions as in this embodiment, the following relationship is established between the transmission bandwidth B and the range resolution Δr. However, θ₁ , Θ₂ Are the radio wave incident angles on the transmitting station side and the receiving station side, respectively, and are the angles shown in FIG.
[0041]
[Equation 3]

[0042]
That is, in order to set the range resolution to an intended value by the multistatic radar, it is necessary to change the transmission bandwidth according to the positional relationship between the transmitting station, the receiving station, and the observation area.
[0043]
Therefore, according to the configuration of this embodiment, the bandwidth calculation means 23 is provided, and the transmission bandwidth is changed according to the positional relationship between the transmission station, the reception station, and the observation region. A high resolution radar image having a desired range resolution can be obtained regardless of the positional relationship.
[0044]
Embodiment 5. FIG.
A synthetic aperture radar apparatus according to Embodiment 5 of the present invention will be described below with reference to FIG. FIG. 10 is a diagram for explaining the configuration of the transmitting station of this apparatus. In the figure, reference numerals 11 to 18 are the same as or equivalent to those in FIG. Reference numeral 24 denotes transmission station selection means. The observation geometry and receiving station of this apparatus are the same as those of the apparatus of the first embodiment.
[0045]
Next, the operation will be described. In FIG. 10, the operations of the transmission unit 18, the transmission antenna 12, and the reference signal transmission antenna 14 are the same as those of the apparatus of the first embodiment. The transmission station selection means 24 selects a transmission station that performs transmission in consideration of the geometric positional relationship among a plurality of transmission stations, reception stations, and observation areas. The transmission station selection procedure is expressed as follows, for example.
[0046]
(ST01)
Select transmitter stations that can see the observation area.
[0047]
(ST02)
The incident power per unit area of the observation area is calculated for each transmitting station in accordance with the following equation, and a transmitting station having a larger value is preferentially selected. However, P_t Is transmission power, G_t Is the gain of the transmitting antenna, R is the distance between the transmitting station and the observation area, θ₁ Is the radio wave incident angle in the observation region. These observation geometries are shown in FIG.
[0048]
[Expression 4]

[0049]
As described above, according to the configuration of this embodiment, it is possible to preferentially select a transmitting station having a large incident power per unit area to the observation region, and thus a high-resolution radar image with excellent S / N is obtained. be able to.
[0050]
Embodiment 6 FIG.
A synthetic aperture radar apparatus according to Embodiment 6 of the present invention will be described below with reference to FIG. In the sixth embodiment, two transmitting stations having an appropriate geometric positional relationship between the transmitting station, the receiving station, and the observation region are selected from the positional relationship between the plurality of known transmitting stations, the receiving station, and the observation region. One of the transmitting stations is configured as shown in FIG. FIG. 12 is a diagram for explaining the configuration of the transmitting station of this apparatus. In the figure, reference numerals 11 to 18 are the same as or equivalent to those in FIG. Reference numeral 25 denotes transmission antenna selection means. Moreover, the observation geometry of this apparatus is shown in FIG. The configuration of the receiving station of this device is the same as that of the device of the first embodiment.
[0051]
Next, the operation will be described. In FIG. 12, the operations of the transmission unit 18, the transmission antenna 12, and the reference signal transmission antenna 14 are the same as those of the apparatus of the first embodiment. The transmission antenna selection unit 25 selects a transmission antenna that radiates radio waves in consideration of a geometric positional relationship among a plurality of transmission antennas, a receiving station, and an observation region.
[0052]
This is the most sensitive when interferometry processing is performed, as in the case of so-called optical stereo vision, when combining results observed from a position with a large expected angle in the direction to be separated (in this case, the vertical direction). It is because it can be made high.
[0053]
Therefore, the selection of the transmission antenna by the transmission antenna selection means 25 is performed as follows, for example.
When viewed from the observation region, the expected angle in the azimuth direction of the transmission antennas of the two selected

transmission stations

16a and 16b is small and the expected angle in the vertical direction is smaller than the plurality of transmission antennas 12c to 12e of the one transmission station 16a. Select a transmit antenna that will be larger. For example, the transmission antenna having the maximum (the expected angle in the vertical direction−the expected angle in the azimuth direction) is selected.
[0054]
As described above, according to the configuration of this embodiment, it is possible to preferentially select a combination of transmitting antennas having a large vertical angle of sight from the observation region, and thus a three-dimensional topographic map with excellent height accuracy. Can be obtained.
[0055]
Embodiment 7 FIG.
A synthetic aperture radar apparatus according to Embodiment 7 of the present invention will be described below with reference to FIG. FIG. 14 is a diagram for explaining the configuration of the transmitting station of this apparatus. In the figure, 11 to 18 and 25 are the same as or equivalent to those of FIG. Moreover, the observation geometry of this apparatus is the same as that of FIG. 13 of Embodiment 6, and the structure of a receiving station is the same as that of FIG.
[0056]
Next, the operation will be described. The apparatus of the seventh embodiment obtains the same effect as that of the sixth embodiment with only one transmitting station. In FIG. 14, the operations of the transmission unit 18, the transmission antenna 12, the reference signal transmission antenna 14, and the transmission antenna selection means 25 a are the same as those of the apparatus of the sixth embodiment. The transmission antenna selection means 25b performs a switching operation as if the transmission antenna 12b and the transmission antenna groups 12c to 12e are different transmission stations.
[0057]
As described above, according to the configuration of this embodiment, two images necessary for the interferometry processing can be obtained by the switching operation of the transmission antenna selection unit 25b in one transmission station, and the transmission antenna selection unit. Since a combination of transmitting antennas having a large angle of view in the vertical direction from the observation area can be preferentially selected in 25a, a three-dimensional topographic map with excellent height accuracy can be obtained with one transmitting station.
[0058]
Embodiment 8 FIG.
A synthetic aperture radar apparatus according to Embodiment 8 of the present invention will be described below with reference to FIG. In the eighth embodiment, a plurality of different observation areas are simultaneously observed, and a three-dimensional topographic map of the plurality of observation areas is obtained by one observation. FIG. 15 is a diagram for explaining the configuration of the receiving station of this apparatus.
, 11 and 15 to 21 are the same as or equivalent to those of FIG. Reference numeral 13 denotes a receiving antenna which is a DBF antenna composed of a plurality of element antennas, and 26 denotes beam forming means. Moreover, the observation geometry of this apparatus is shown in FIG. In the figure, reference numerals 11 to 17 are the same as or equivalent to those of the first embodiment. The configuration of each transmitting station is the same as that of the apparatus of the second embodiment.
[0059]
Next, the operation will be described. The receiving antenna 13 is a DBF antenna, and the output of each element antenna is amplified by the receiving unit 19 and then input to the beam forming means 26. The beam forming unit 26 forms a reception beam in a desired direction by a well-known beam steering operation of the following formula. Where S ′ is the beam output at the angle η, i is the element antenna number of the DBF antenna, S_i Is the output signal of the i-th element antenna, d is the element spacing, and λ is the wavelength. Although one-dimensional beam formation is illustrated here, this equation can be easily extended to a two-dimensional case.
[0060]
[Equation 5]

[0061]
The beam steering operation can be performed in parallel in a plurality of directions, so that a plurality of reception beams can be simultaneously formed from the reception signal obtained by the DBF antenna. The received signals of the respective beams are input to the pulse discriminating means 20 and operate in the same manner as described in FIG. 3 in the first embodiment.
[0062]
That is, as shown in FIG. 16, signals reflected from a plurality of observation areas can be simultaneously received and processed by one receiving station.
[0063]
As described above, according to the configuration of the eighth embodiment, it is possible to simultaneously obtain a high-resolution radar image and a three-dimensional topographic map of a plurality of observation areas by one receiving station by one simultaneous observation.
[0064]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
[0065]
  thisAccording to the invention, in a multi-static synthetic aperture radar apparatus in which a transmitting station and a receiving station are separately provided on a mobile platform such as the ground, an aircraft, or a satellite, a single receiving station is provided, so that There is an effect of realizing a synthetic aperture radar device that can obtain a three-dimensional topographic map by observation.
[0066]
  Also,In a multi-static synthetic aperture radar device that is configured by separately providing a transmitting station and a receiving station on a mobile platform such as the ground, an aircraft, or a satellite, a configuration using one transmitting station is used. There is no need for discrimination means, and it is possible to realize a synthetic aperture radar apparatus that can obtain a three-dimensional topographic map with a single observation at a receiving station with a simple configuration.
[0067]
Alternatively, it is possible to realize a synthetic aperture radar device that can obtain a three-dimensional topographic map with one observation.
[0068]
  Also,There is an effect that a high-resolution radar image having a desired range resolution can be obtained by one observation regardless of the positional relationship between the transmitting station, the receiving station, and the observation region.
[0069]
  Also,There is an effect that a high-resolution radar image having an excellent S / N can be obtained by one observation.
[0070]
  Also,There is an effect that a three-dimensional topographic map with excellent height accuracy can be obtained by one observation.
[0071]
  Also,One transmitting station has an effect of obtaining a three-dimensional topographic map with excellent height accuracy.
[0072]
  further,There is an effect that a plurality of different observation areas can be observed at the same time, and a three-dimensional topographic map of the plurality of observation areas can be obtained simultaneously by one receiving station in one observation.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an observation geometry of a synthetic aperture radar device according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a transmission station of the synthetic aperture radar device according to the first embodiment of the present invention.
FIG. 3 is a configuration diagram of a receiving station of the synthetic aperture radar device according to the first embodiment of the present invention.
FIG. 4 is an explanatory diagram of an observation geometry of a synthetic aperture radar device according to Embodiment 2 of the present invention.
FIG. 5 is a configuration diagram of a transmission station of a synthetic aperture radar apparatus according to Embodiment 2 of the present invention.
FIG. 6 is a configuration diagram of a receiving station of the synthetic aperture radar device according to the second embodiment of the present invention.
FIG. 7 is a configuration diagram of a transmitting station of a synthetic aperture radar apparatus according to Embodiment 3 of the present invention.
FIG. 8 is a configuration diagram of a transmitting station of a synthetic aperture radar device according to a fourth embodiment of the present invention.
FIG. 9 is an explanatory diagram of an observation geometry of the synthetic aperture radar device according to the fourth embodiment of the present invention.
FIG. 10 is a configuration diagram of a transmitting station of a synthetic aperture radar device according to a fifth embodiment of the present invention.
FIG. 11 is an explanatory diagram of an observation geometry of the synthetic aperture radar device according to the fifth embodiment of the present invention.
FIG. 12 is a configuration diagram of a transmitting station of a synthetic aperture radar device according to a sixth embodiment of the present invention.
FIG. 13 is an explanatory diagram of an observation geometry of the synthetic aperture radar device according to the sixth embodiment of the present invention.
FIG. 14 is a configuration diagram of a transmitting station of a synthetic aperture radar device according to a seventh embodiment of the present invention.
FIG. 15 is a configuration diagram of a receiving station of a synthetic aperture radar device according to an eighth embodiment of the present invention.
FIG. 16 is an explanatory diagram of an observation geometry of the synthetic aperture radar device according to the eighth embodiment of the present invention.
FIG. 17 is a configuration diagram of a conventional synthetic aperture radar apparatus.
FIG. 18 is an explanatory diagram of an observation geometry of a conventional synthetic aperture radar device.
[Explanation of symbols]
1, 2 transmit / receive antenna, 3 transmit / receive antenna group, 4, 5 transmit / receive unit,
6 image processing unit, 7 interference processing unit, 8 landform change analysis processing unit,
9 Elevation difference detector, 10 database, 11 observation area,
12 transmitting antenna, 13 receiving antenna, 14 reference signal transmitting antenna, 15 reference signal receiving antenna, 16 transmitting station, 17 receiving station, 18 transmitting unit, 19 receiving unit, 20 pulse discrimination means, 21 demodulator, 22 transmission synchronization Means, 23 bandwidth calculating means, 24 transmitting station selecting means, 25 transmitting antenna selecting means, 26 beam forming means.

Claims

A first transmitting antenna and a receiving station for transmitting a high-frequency pulse to an observation region in a multi-static synthetic aperture radar apparatus configured by separately providing a transmitting station and a receiving station on a mobile platform such as the ground, an aircraft, or a satellite A plurality of antennas installed on the ground, each having a second transmission antenna for transmitting a reference signal to the navel and each of the first transmission antennas of at least two transmission stations being spaced apart by a predetermined baseline length A transmitting station; a first receiving antenna that simultaneously receives high-frequency pulses from the plurality of transmitting stations reflected from the observation region; a second receiving antenna that simultaneously receives reference signals from the plurality of transmitting stations; and A pulse discriminating means for separating a series of pulse trains from the first receiving antenna and the second receiving antenna for each transmitting station; A demodulator for demodulating the received signal received by the first receiving antenna in synchronization with the reference signal from each transmitting station received by the receiving antenna, and comprising a receiving station installed on the mobile platform, Based on the output of the demodulator, an image processing unit obtains a high-resolution radar image, and an interferometry process that obtains the height of the terrain in the interference processing unit from the phase difference between the obtained at least two synthetic aperture radar images. A synthetic aperture radar apparatus characterized by obtaining a three-dimensional topographic map in one observation.

A first transmitting antenna and a receiving station for transmitting a high-frequency pulse to an observation region in a multi-static synthetic aperture radar apparatus configured by separately providing a transmitting station and a receiving station on a mobile platform such as the ground, an aircraft, or a satellite A plurality of antennas installed on the ground, each having a second transmission antenna for transmitting a reference signal to the navel and each of the first transmission antennas of at least two transmission stations being spaced apart by a predetermined baseline length A transmission station, transmission synchronization means for controlling the transmission timing of the high-frequency pulse from the plurality of transmission stations to the observation region so that reflections from the observation region do not interfere with each other, and the plurality of transmissions reflected from the observation region A first receiving antenna that receives high-frequency pulses from the station and a second receiver that receives reference signals from the plurality of transmitting stations. At least an antenna and a demodulator that demodulates a received signal received by the first receiving antenna in synchronization with a reference signal from each transmitting station received by the second receiving antenna, and is installed on the mobile platform A high resolution radar image is obtained by the image processing unit based on the output of the demodulator, and the height of the topography is obtained by the interference processing unit from the phase difference between the obtained synthetic aperture radar images. A synthetic aperture radar apparatus characterized in that a three-dimensional topographic map is obtained by one observation by interferometry processing.

The synthetic aperture radar apparatus according to claim 1 or 2, wherein a transmission bandwidth capable of obtaining a predetermined range resolution is calculated based on a geometric positional relationship between the transmitting station and the receiving station with respect to the observation region, and transmission from the transmitting station is performed. A synthetic aperture radar apparatus comprising bandwidth calculating means for setting a bandwidth.

In the synthetic aperture radar device according to any one of claims 1 to 3 , a transmitting station that can see the observation region is selected and selected in accordance with a change in a geometric positional relationship between the transmission station, the receiving station, and the observation region. Synthetic aperture radar apparatus comprising transmission station selection means for calculating the incident power to the observation area of the transmission station and switching the transmission station so as to preferentially select and transmit the transmission station having a large incident power .

2. The synthetic aperture radar apparatus according to claim 1, wherein a plurality of transmitting stations having an appropriate geometrical positional relationship between a transmitting station, a receiving station, and an observation area are replaced with a first transmitting antenna of one transmitting station. First transmission antenna and transmission antenna selection means for switching to use one of the plurality of first transmission antennas. The first of the two transmission stations when viewed from the observation region A synthetic aperture radar apparatus, wherein one of the plurality of first transmission antennas of the one transmission station is selected and used so that a vertical angle of the transmission antenna of the first transmission antenna is increased.

In synthetic aperture radar system according to claim 1 Symbol placement, geometric positional relationship for the appropriate one of the transmitting station of the observation area and transmitting and receiving stations, a plurality of in place of the first transmission antenna of the transmitting station First transmission antenna selection means for switching to use one selected from the first transmission antenna and the plurality of first transmission antennas and the first transmission antenna provided in addition to the plurality of first transmission antennas A transmission antenna, and a second transmission antenna selection means for switching between the first transmission antenna and the plurality of first transmission antennas, in addition to the plurality of first transmission antennas when viewed from the observation region. One of the plurality of first transmission antennas is selected so that the expected angle in the vertical direction of the first transmission antenna of the first transmission antenna and the first transmission antenna of the plurality of first transmission antennas is increased. Use Synthetic aperture radar system, characterized in that.

A multi-static synthetic aperture radar apparatus comprising a transmitting station and a receiving station separately provided on a mobile platform such as the ground, an aircraft, or a satellite, wherein the first transmitting antenna transmits a high-frequency pulse to an observation region; A second transmitting antenna for transmitting the reference signal to the receiving station; a transmitting station installed on the ground; a first receiving antenna for receiving high-frequency pulses from the transmitting station reflected from the observation area; and A second receiving antenna for receiving a reference signal from the transmitting station; and a demodulator for demodulating the received signal received by the first receiving antenna in synchronization with the reference signal from the transmitting station received by the second receiving antenna; And the first receiving antennas of each of the at least two receiving stations are arranged at a predetermined baseline length apart. A plurality of receiving stations installed on different mobile platforms, and a high-resolution radar image obtained by an image processing unit based on the output of the demodulator, and two synthetic aperture radars obtained by at least two receiving stations In a synthetic aperture radar apparatus that obtains a three-dimensional topographic map in one observation by interferometry processing in which the height of the topography is obtained by the interference processing unit from the phase difference of the image, the geometry of the transmitting station, the receiving station, and the observation area For one transmitting station having an appropriate positional relationship, one of the plurality of first transmitting antennas and the plurality of first transmitting antennas is selected and used instead of the first transmitting antenna of the transmitting station. First transmission antenna selection means for switching to the first transmission antenna, the first transmission antenna provided in addition to the plurality of first transmission antennas, the first transmission antenna, and the plurality of first transmission antennas. Second transmission antenna selection means for switching between the first transmission antenna and the plurality of first transmission antennas provided in addition to the plurality of first transmission antennas when viewed from the observation region. A synthetic aperture radar apparatus, wherein one of the plurality of first transmission antennas is selected and used so that a vertical angle of view of one first transmission antenna is increased.

The transmit station and a receiving station, the ground, in synthetic aperture radar device multistatic system constituting provided by separating the mobile platform such as an aircraft or satellite, receiving a first transmission antenna for transmitting radio frequency pulses into the observation region A second transmitting antenna that transmits the reference signal to the station, and a plurality of pairs of transmitting stations that transmit high-frequency pulses to each of the plurality of observation regions; A digital beam forming antenna (referred to as a DBF antenna) composed of a plurality of element antennas that simultaneously receives high-frequency pulses from a pair of transmitting stations and a second reception that simultaneously receives reference signals from the plurality of pairs of transmitting stations. The antenna and the output of the DBF antenna are input, and the beam is operated to , A beam discriminating means for separating a series of pulse trains from the DBF antenna and the second receiving antenna for each transmitting station, and a reference signal from each transmitting station received by the second receiving antenna A receiving station having at least a demodulator that demodulates the received signal received by the DBF antenna, and simultaneously observes the plurality of different observation areas, and performs high resolution in the image processing unit based on the output of the demodulator. A radar image is obtained, and a three-dimensional topographic map is obtained in one observation by interferometry processing in which the height of the topography is obtained by the interference processing unit from the phase difference between at least two obtained synthetic aperture radar images. Synthetic aperture radar device.