Method of processing spotlight SAR raw data

US 6,222,933 B1
Filed: 12/21/1998
Issued: 04/24/2001
Est. Priority Date: 12/22/1997
Status: Expired due to Term

First Claim

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1. A method of processing two-dimensional spotlight SAR raw data into image data, comprising sequential steps of:

(3.1) dividing the spotlight SAR raw data into azimuth sub-aperture data;

(3.2) transforming the sub-aperture data, via short azimuth FFTS, into azimuthal frequency data, whereby the raw data comprises two-dimensional time data;

(3.3, 3.4) multiplying the two-dimensional data by a frequency-scaling function H_f(f_a, t_r;

r_o) defined by $\begin{matrix} \begin{matrix} H_{r} (f_{a}, t_{r}; r_{o}) = \exp [j \cdot \frac{2 \cdot π \cdot k_{r}}{c_{o}} \cdot β (f_{a}) \cdot t_{r}^{2}] \cdot \\ \exp [j \cdot 2 π \cdot \frac{β^{2} - 1}{c_{o}^{2} \cdot β^{3}} \cdot r_{o} \cdot λ \cdot k_{r}^{2} \cdot {(t_{r} - \frac{2 \cdot r_{ref}}{c_{o}})}^{2}] \end{matrix} & (5) \end{matrix}$

wherein f_ais azimuth frequency, t_ris range time, r₀is a shortest distance from a target, k_ris a modulation rate of the transmitted pulses in the range, r_refis a reference range, f_ris a range frequency, c₀is the speed of light, λ

is wavelength, and wherein β

is given by $\begin{matrix} β (f_{a}) = \sqrt{1 - {(\frac{f_{a} λ}{2 V})}^{2}} & (7) \end{matrix}$

where V is speed, whereby a secondary range compression of the two-dimensional data is performed;

(3.5) transforming the two-dimensional data, via short range FFTs, into two-dimensional frequency data (azimuthal and range frequency domain);

(3.6, 3.7) multiplying the two-dimensional frequency data by a residual-video-phase correction function H_RVPgiven by $\begin{matrix} H_{RVP} (f_{r}) = \exp [- j \cdot π \cdot \frac{f_{r}^{2}}{β \cdot k_{r}}] & (8) \end{matrix}$ (3.8) transforming the two-dimensional frequency data, via short range IFFTs, back into range time/azimuthal frequency domain;

(3.9) multiplying the two-dimensional data by an inverse frequency-scaling function H_ifgiven by $\begin{matrix} \begin{matrix} H_{If} (f_{a}, t_{r}) = \exp [π \cdot k_{r} \cdot (β^{2} - β) \cdot t_{r}^{2}] \cdot \\ \exp [j \cdot \frac{4 \cdot π \cdot k_{r}}{c_{o}} \cdot r_{ref} \cdot (1 - β) \cdot t_{r}] \end{matrix} & (9) \end{matrix}$

whereby a block shift is performed;

(3.11) transforming the two-dimensional data, via long range FFTs, into two-dimensional frequency domain;

multiplying the two-dimensional frequency data by the phase-correction function H_koorgiven by $\begin{matrix} H_{korr} (f_{a}, f_{r}) = \exp [- j \cdot \frac{4 \cdot π \cdot k_{r}}{c_{o}} \cdot \frac{2 \cdot r_{ref}}{c_{o}} \cdot (1 - β) \cdot (r_{ref} - \frac{f_{r} \cdot c_{o}}{2 \cdot k_{r}})] & (11) \end{matrix}$ (3.15) subsequently multiplying the two-dimensional frequency data by an azimuth-scaling function H_a(f_a, f_r) given by $\begin{matrix} \begin{matrix} H_{a} (f_{a}, f_{r}) = \exp [j 4 \cdot \frac{π}{λ} \cdot (r_{ref} - \frac{f_{r} \cdot c_{o}}{2 \cdot k_{r}}) \cdot (β - 1)] \cdot \\ \exp [j \cdot \frac{π}{k_{a, scL}} \cdot f_{a}^{2}] \end{matrix} & (12) \end{matrix}$

wherein k_a,sclis a scaling Doppler rate;

(3.16) transforming the two-dimensional frequency data, via short azimuth FFTs, into the range frequency/azimuthal time domain;

(3.17) re-assembling the azimuth sub-apertures;

(3.18, 3.19) multiplying the two-dimensional data of the azimuth sub-apertures by a de-ramping function H_der(t_a) given by

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Abstract

For two-dimensional processing of spotlight SAR data into exact image data, the spotlight SAR raw data are divided into azimuth sub-apertures and transformed into the range-time/azimuth-frequency domain through short azimuth FFTs. The obtained data are multiplied by a frequency-scaling function H_f(f_a, t_r; r₀) and transformed into the two-dimensional frequency domain through short range FFTs, multiplied by an RV-phase-correction function H_RVP(f_r) and subsequently transformed back into the range time/azimuth-frequency domain through short range IFFTs. The data formed in this manner are multiplied by the inverse frequency-scaling function H_g(f_a, f_r), then transformed back into the two-dimensional frequency domain, multiplied by the phase-correction function H_korr(f_a, f_r) and the azimuth-scaling function H_a(f_a, f_r), and transformed back into the range-frequency/azimuth-time domain through short azimuth FFTS. Then the azimuth sub-apertures are re-assembled, multiplied by a de-ramping function H_der(t_a) and transformed into the two-dimensional frequency domain through long azimuth FFTs.

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2 Claims

1. A method of processing two-dimensional spotlight SAR raw data into image data, comprising sequential steps of:
- (3.1) dividing the spotlight SAR raw data into azimuth sub-aperture data;
  
  (3.2) transforming the sub-aperture data, via short azimuth FFTS, into azimuthal frequency data, whereby the raw data comprises two-dimensional time data;
  
  (3.3, 3.4) multiplying the two-dimensional data by a frequency-scaling function H_f(f_a, t_r;
  
  r_o) defined by $\begin{matrix} \begin{matrix} H_{r} (f_{a}, t_{r}; r_{o}) = \exp [j \cdot \frac{2 \cdot π \cdot k_{r}}{c_{o}} \cdot β (f_{a}) \cdot t_{r}^{2}] \cdot \\ \exp [j \cdot 2 π \cdot \frac{β^{2} - 1}{c_{o}^{2} \cdot β^{3}} \cdot r_{o} \cdot λ \cdot k_{r}^{2} \cdot {(t_{r} - \frac{2 \cdot r_{ref}}{c_{o}})}^{2}] \end{matrix} & (5) \end{matrix}$
  
  wherein f_ais azimuth frequency, t_ris range time, r₀is a shortest distance from a target, k_ris a modulation rate of the transmitted pulses in the range, r_refis a reference range, f_ris a range frequency, c₀is the speed of light, λ
  
  is wavelength, and wherein β
  
  is given by $\begin{matrix} β (f_{a}) = \sqrt{1 - {(\frac{f_{a} λ}{2 V})}^{2}} & (7) \end{matrix}$
  
  where V is speed, whereby a secondary range compression of the two-dimensional data is performed;
  
  (3.5) transforming the two-dimensional data, via short range FFTs, into two-dimensional frequency data (azimuthal and range frequency domain);
  
  (3.6, 3.7) multiplying the two-dimensional frequency data by a residual-video-phase correction function H_RVPgiven by $\begin{matrix} H_{RVP} (f_{r}) = \exp [- j \cdot π \cdot \frac{f_{r}^{2}}{β \cdot k_{r}}] & (8) \end{matrix}$ (3.8) transforming the two-dimensional frequency data, via short range IFFTs, back into range time/azimuthal frequency domain;
  
  (3.9) multiplying the two-dimensional data by an inverse frequency-scaling function H_ifgiven by $\begin{matrix} \begin{matrix} H_{If} (f_{a}, t_{r}) = \exp [π \cdot k_{r} \cdot (β^{2} - β) \cdot t_{r}^{2}] \cdot \\ \exp [j \cdot \frac{4 \cdot π \cdot k_{r}}{c_{o}} \cdot r_{ref} \cdot (1 - β) \cdot t_{r}] \end{matrix} & (9) \end{matrix}$
  
  whereby a block shift is performed;
  
  (3.11) transforming the two-dimensional data, via long range FFTs, into two-dimensional frequency domain;
  
  multiplying the two-dimensional frequency data by the phase-correction function H_koorgiven by $\begin{matrix} H_{korr} (f_{a}, f_{r}) = \exp [- j \cdot \frac{4 \cdot π \cdot k_{r}}{c_{o}} \cdot \frac{2 \cdot r_{ref}}{c_{o}} \cdot (1 - β) \cdot (r_{ref} - \frac{f_{r} \cdot c_{o}}{2 \cdot k_{r}})] & (11) \end{matrix}$ (3.15) subsequently multiplying the two-dimensional frequency data by an azimuth-scaling function H_a(f_a, f_r) given by $\begin{matrix} \begin{matrix} H_{a} (f_{a}, f_{r}) = \exp [j 4 \cdot \frac{π}{λ} \cdot (r_{ref} - \frac{f_{r} \cdot c_{o}}{2 \cdot k_{r}}) \cdot (β - 1)] \cdot \\ \exp [j \cdot \frac{π}{k_{a, scL}} \cdot f_{a}^{2}] \end{matrix} & (12) \end{matrix}$
  
  wherein k_a,sclis a scaling Doppler rate;
  
  (3.16) transforming the two-dimensional frequency data, via short azimuth FFTs, into the range frequency/azimuthal time domain;
  
  (3.17) re-assembling the azimuth sub-apertures;
  
  (3.18, 3.19) multiplying the two-dimensional data of the azimuth sub-apertures by a de-ramping function H_der(t_a) given by
- View Dependent Claims (2)
- - 2. The use of a method according to claim 1 for two-dimensional processing of SONAR and seismic raw data with the stripmap, spotlight and hybrid modes.

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Current Assignee
Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
Original Assignee
Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
Inventors
Mittermayer, Josef, Moreira, Alberto
Primary Examiner(s)
Bella, Matthew C.
Assistant Examiner(s)
CHOOBIN, BARRY

Application Number

US09/217,571
Time in Patent Office

855 Days
Field of Search

382/109, 382/48, 382/25, 382/293, 382/28, 342/192, 342/196, 342/25, 342/161
US Class Current

382/109
CPC Class Codes

G01S 13/904   SAR modes

G01S 13/9052   Spotlight mode

G01S 13/9054   Stripmap mode

G01S 7/2883   using FFT processing

Method of processing spotlight SAR raw data

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Method of processing spotlight SAR raw data

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Abstract

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