High speed synthetic radar processing system

• US 4,910,520 A
• Filed: 07/30/1987
• Issued: 03/20/1990
• Est. Priority Date: 04/08/1985
• Status: Expired due to Fees

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Victor, Arnold E., Rosen, Robert A., Krikorian, Kapriel V.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/080,181
• Time in Patent Office: 964 Days
• Field of Search: 342/25
• US Class Current: 342/25.00A
• CPC Class Codes: G01S 13/9004 SAR image acquisition techniques

Abstract

A synthetic aperture radar processing system receiving return data from a plurality of transmitted pulses which utilizes frequency alignment for partitioning the received data into patches of data in an orderly sequence, a plurality of patches of data being formed in each of a plurality of range subswaths and being sequentially aligned in range columns. For each subswath, the return data is filtered in patch filters having wide bandwidths and passband overlaps selected so that each patch of data is totally included within a passband. The patch filters are selected for each subswath to provide sequential columns of data. Each patch of data for each subswath is then frequency shifted to an interpolator narrow band filter having a passband selected so that data outside of each patch is eliminated. As a result, the patches of data at the outputs of the interpolators are in the proper sequence for each column to be further processed without the addressing and bookkeeping problems associated with partitioning of data into patches with conventional patch filter banks.

Claims

1. The method of partitioning and processing data in a synthetic aperture radar mapping system for use with a moving craft receiving a time sequence of pulse return data from each of a plurality of pulses sequentially transmitted at a predetermined PRF to a surface being mapped and having range and cross range dimensions, the return data from each transmitted pulse being sequentially sampled to form sequence of sample words at a rate determined by the radar PRF, said surface including swaths each divided into range subswaths with each subswath including adjacent cross range patches with corresponding patches in all subswaths forming columns in range, said system forming a sequence of sampled data from the pulse return data from each transmitted pulse, said method comprising the steps of:

dechirping said sequences of sampled data for each subswath into a plurality of doppler frequency bands, each representing a patch filter band;

patch filtering said sequences of sampled data for each subswath to pass data in said patch filter band with said sequences of data for each patch passing through one of said filter bands, wherein said patch filtering includes the steps of;

skipping a selected number of sequences of sampled data to provide a reduced number of sequences of sampled data for each patch, and

data turning the reduced number of sequences of sampled data to provide one half of the sequences of sampled data for each patch to be applied to the patch filtering steps;

sequentially selecting patch filter bands for each subswath that pass corresponding column data;

frequency shifting the data passed through each of said patch filter bands for each subswath to a selected center frequency;

interpolator filtering for passing at said selected center frequency, the sequences of data passed through said patch filter bands in a time sequence corresponding to the positions of said columns; and

,

processing the sequences of data that are interpolator filtered for forming pixel display data in a time sequence corresponding to the positions of said columns.

2. The method of claim 1 wherein the step of interpolator filtering includes the step of providing a sampling rate for said sequences of data provided by said patch filtering step that is lower than said sampling rate determined by said radar PRF, said skipping step and said data turning step.

3. The method of data partitioning for use with a synthetic aperture radar mapping system in which pulses of energy are repeatedly transmitted from a moving craft to a surface being mapped from which sequences of pulse return data are received, adjacent areas of said surface being swaths with each swath including a plurality of range subswaths and with each subswath being divided into a plurality of cross range patches aligned in range columns in said plurality of said subswaths, said mapping system converting said return data received in response to each transmitted pulse to a sequence of words, said method comprising the steps of:

subswath filtering each of said sequence of words to provide sequence of words for each subswath;

azimuth dechirping each of said sequence of words to provide a doppler frequency band for each sequence of said words derived from data received from each patch of each subswath, the frequency bands for subswaths at increasing range decreasing in width;

patch filtering with frequency overlapping patch filters each sequence of words for each patch;

selecting patch filter numbers for each patch;

selecting a filter output word for each patch in sequence in said swath to provide sequences of patch filter output words;

frequency shifting the sequences of patch filter output words so that the sequences of output words of each patch are centered at a predetermined selected frequency;

interpolator filtering at said selected center frequency with band widths of decreasing size for subswaths of increasing range sequentially for each patch of each subswath, each patch filter providing a sequence of interpolator output words;

final range filtering each completed sequence of interpolator output words to provide a range sequence of a selected number of range words for each sequence of interpolator output words for each patch of each subswath; and

final cross range filtering of the range words of each range sequence to provide a selected number of cross range words for each sequence of interpolator output words for each patch of each subswath.