T.I. Lukowski

Synthetic aperture radar calibration using reference reflectors

A simple expression for the terrain backscatter coefficient is derived in terms of the integrated power of an adjacent known radar reflector in a synthetic aperture radar (SAR) image. It is shown that this technique for SAR image calibration is independent of the radar system focus or partial coherence and thereby possesses an important advantage over the usual technique, which relies on an estimate of the peak of the reflector impulse response. Results from airborne SAR overflights of corner reflectors and active radar calibrators are used to demonstrate the validity and consistency of the method and to show that the method is robust under defocus caused by an incorrect FM rate or inadequate motion compensation of data collected during turbulence. It is also shown that the fading errors associated with the integral method are comparable to or slightly worse than those associated with the peak estimation method. However, this small disadvantage is outweighed by the fact that the integral method is independent of actual resolution. >

RADARSAT image quality and calibration — Update

Abstract This paper reviews image quality and radiometric calibration aspects of the first two years of operation of RADARSAT. This includes the calibration of almost all beams (a total of more than 25 beams when considering shifted positions of each of the Fine beams), and the stability and calibration accuracies achieved during the mission to date. The measurements show that the SAR performance is better than the specifications. In September 1997, RADARSAT underwent a major configuration change to accommodate the Antarctic Mapping Mission for a period of about five weeks. To achieve this, the spacecraft was rotated to allow imaging from a left-looking geometry. The image quality and calibration results for the left-looking mode are also discussed.

Plans for RADARSAT image data calibration

Abstract RADARSAT, the first Canadian earth observation satellite, is scheduled for launch in 1995. The mission is to provide to users calibrated C-band HH polarized Synthetic Aperture Radar (SAR) data products for five years, at different incidence angles, resolution and area coverage. The SAR is also designed to operate in the ScanSAR mode by combining different elevation beams. Emphasis in the RADARSAT Program is provision of operationally calibrated products which insures targets can be compared radiometrically within each scence and between scences. In order to maintain end-to-end radiometric quality for the mission life, plans are to perform external calibration routinely using precision transponders and homogeneous targets. The calibration data will be analyzed off-line in the calibration workstation and resulting calibration parameters update will be provided to the ground processor to generate calibrated products. The short term variations in the gain of the sensor electronics will be tracked by the on board internal calibration system and these calibration data will be transmitted to the ground with the radar signal data. This allows the processor to automatically compensate for radar gain variations in between the external calibration periods and thus maintain the required radiometric accuracy. This paper describes the calibration requirements for the mission and plans for internal and external calibrations. An outline of the image quality management is also presented.

RADARSAT-1 image quality and calibration — a continuing success

Abstract The Canadian earth observation satellite, RADARSAT-1 was launched on November 4, 1995 with the first image acquired on November 28 of that year. After commissioning it was put into routine operation on April 1, 1996. Since then more than four years of successful operation have been completed, utilizing data for their intended applications. Significant effort has been extended in the provision of radiometrically and geometrically calibrated products to users by the Canadian Data Processing Facility (CDPF). Particular emphasis has been on the maintenance of image quality and calibration as monitored using images of the Amazon Rainforest and of the RADARSAT-1 Precision Transponders (RPT). This first part of the paper will review the image quality and calibration evolution of RADARSAT-1, complementing previously presented reviews on this subject. Data will be given on various image quality parameters related to impulse response, location error, antenna pattern and noise equivalent measures, and on calibration accuracy as achieved to date. Recent work on calibration and image quality improvements for ScanSAR products are also presented. The latter part of the paper describes methodologies developed for maintenance of radiometric calibration performance of RADARSAT-1, including a statistical technique useful for early detection of radiometric problems associated with single calibrated beams.

RADARSAT elevation antenna pattern determination

The operations plan for RADARSAT is based on implicit calibration of the imagery products from this sensor system. The determination of the antenna gain patterns in elevation for RADARSAT is a critical step in the radiometric calibration of this imagery. The shapes of the antenna patterns in elevation were derived from imagery collected over the South American rain forests of Brazil and Colombia with a consistency on the order of /spl plusmn/0.2 dB. The absolute levels of the patterns have been determined by superposing the shapes on results from a set of precision radar ground targets known as the RADARSAT Precision Transponders. As pattern revisions are determined, they are included operationally in the determination of the corrections that are required in the Canadian Data Processing Facility to create radiometrically calibrated image products.

Maintaining image quality and calibration of RADARSAT-1 CDPF products

RADARSAT-1 was launched in November 1995 with the first image acquired on November 28 of that year. After commissioning, it was put into routine operation on April 1, 1996. Significant effort has been expended in the provision of radiometrically and geometrically calibrated products to users by the Canadian Data Processing Facility (CDPF). Particular emphasis has been on the determination of the antenna gain patterns and on image quality as measured using images of the Amazon rainforest and of the RADARSAT-1 Precision Transponders (RPT). This paper reviews stability and calibration accuracy as achieved to date, image quality results and includes the latest developments for ScanSAR products.

RADARSAT image quality and calibration performance-update

This paper reviews image quality and radiometric calibration aspects of the first two years of operation of RADARSAT. This includes the initialization of almost all beams, stability and calibration accuracies achieved during the mission to date. In September 1997, RADARSAT underwent a major configuration change to accommodate the Antarctic Mapping Mission for a period of about five weeks. To achieve this, the spacecraft was rotated to allow imaging from a left-looking geometry. The image quality and calibration results for the left-looking mode are also discussed.

Calibration and image quality performance results of RADARSAT

Abstract The Canadian earth observation satellite, RADARSAT, was launched in late 1995. The aim of this space borne Synthetic Aperture Radar (SAR) program is to provide C-band HH polarized SAR data products for five years at varying incidence angles, resolutions and area coverages. The system has been designed to produce imagery using single beams in elevation and also to operate in the ScanSAR mode by combining different elevation beams. SAR images have been obtained and were used to measure system performance during the Beam Qualification Phase. The measured image quality parameters for single beam products dealing with all aspects of image quality except radiometric calibration have been found to meet and exceed the system specifications. Based on the system performance and on completion of the commissioning activities, the Initial Operational Capability for the system was declared in April 1996.

RADARSAT-2; are its technical capabilities expected to provide potential for remote sensing applications ?

In this paper, we preview and demonstrate how the technical improvements included in RADARSAT-2 will impact the systems potential utility for 32 applications in the fields of agriculture, cartography, disaster management, forestry, geology, hydrology, oceans, and sea and land ice.

Calibration for RADARSAT

RADARSAT is an operational synthetic aperture radar (SAR) in space scheduled for launch in 1995. The mission is to be 5 years long and will deliver relatively calibrated data products to users. This paper describes the calibration methodology to achieve and maintain the end-to-end image quality requirements of the mission. An outline of the planned image quality management is also given.<<ETX>>