HMPF is a computer program that implements a modified polar-format algorithm for processing data from spaceborne synthetic-aperture radar (SAR) systems. Unlike prior polar-format processing algorithms, this algorithm is based on the assumption that the radar signal wavefronts are spherical rather than planar. The algorithm provides for resampling of SAR pulse data from slant range to radial distance from the center of a reference sphere that is nominally the local Earth surface. Then, invoking the projection-slice theorem, the resampled pulse data are Fourier-transformed over radial distance, arranged in the wavenumber domain according to the acquisition geometry, resampled to a Cartesian grid, and inverse-Fourier-transformed. The result of this process is the focused SAR image. HMPF, and perhaps other programs that implement variants of the algorithm, may give better accuracy than do prior algorithms for processing strip-map SAR data from high altitudes and may give better phase preservation relative to prior polar-format algorithms for processing spotlight-mode SAR data.
This program was written by Curtis Chen of Caltech for NASA’s Jet Propulsion Laboratory.
This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393- 3425. Refer to NPO-30906.
This Brief includes a Technical Support Package (TSP).
Modified Polar-Format Software for Processing SAR Data
(reference NPO-30906) is currently available for download from the TSP library.
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Overview
The document presents a technical support package detailing a Modified Polar Format Algorithm for processing spaceborne synthetic aperture radar (SAR) data, authored by Curtis W. Chen and prepared under the auspices of NASA's Jet Propulsion Laboratory (JPL). This algorithm is designed to improve the processing of SAR data by assuming a spherical reference surface, which is particularly beneficial for sensors operating at medium Earth orbit (MEO) altitudes or higher, where the curvature of the Earth significantly impacts data accuracy.
The introduction highlights the limitations of standard polar format algorithms, which typically assume planar signal wavefronts. The modified algorithm aims to enhance phase preservation, especially for spotlight-mode data, and is also applicable to ScanSAR data where targets experience considerable range migration during burst periods. This improvement is crucial for achieving high-resolution imaging and accurate data representation.
The document outlines the mathematical framework and coordinate systems used in the algorithm, defining a body-fixed Cartesian coordinate system with the origin at the Earth's center. It discusses the effects of orbital motion on image focus, particularly in circular orbits, and emphasizes the importance of accounting for both vertical and horizontal curvature in SAR data processing.
Key results from the analysis indicate that the algorithm can effectively manage the complexities introduced by the Earth's curvature, leading to better image quality and more reliable data interpretation. The document also references various processing steps required for different SAR modes, including spotlight, stripmap, hybrid spotlight-stripmap, and ScanSAR modes, illustrating the versatility of the algorithm in handling diverse imaging scenarios.
In conclusion, the Modified Polar Format Algorithm represents a significant advancement in SAR data processing, offering improved accuracy and phase preservation for spaceborne sensors. The document serves as a comprehensive guide for researchers and engineers in the field, providing insights into the algorithm's development, application, and potential benefits for future SAR missions. For commercial inquiries, Don Hart at Caltech is the designated contact for licensing opportunities.
