Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [THP-4 MICROWAVE SENSING]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: CONSIDERATIONS FOR SAR CALIBRATION UNIQUE TO ORBITAL SYSTEMS. R. Keith Raney

Document type:: Multivolume work

Structure type:: Chapter

709 CONSIDERATIONS FOR SAR CALIBRATION UNIQUE TO ORBITAL SYSTEMS R. Keith Raney Chief Radar Scientist Canada Centre for Remote Sensing Ottawa, Ontario, Canada ISPRS Commission VII ABSTRACT For calibration purposes, quantitative expressions are required for the response of a synthetic aperture radar (SAR) to both point and distributed scatterers. The orbital geometry for satellite SAR systems needs to be included in the analysis. Unlike the "flat Earth" case, the spacecraft velocity and the beam footprint velocity are different, and enter key expressions in different ways. The impulse response width of a point reflector is improved by the velocity ratio, and the peak of the impulse response is enhanced over that predicted from the flat Earth model. When imagery of a distributed scene observed by an orbital SAR is to be calibrated by comparison to the impulse response of a reference point scatterer, the velocity ratio enters the expression for peak power, but does not enter when an integral is used over the impulse response. The velocity ratio effect is about -0.5 dB for typical systems, and thus is significant when compared to modern SAR calibration goals. Image signal to noise ratio is dependent on footprint velocity, but the mean clutter to noise ratio for distributed scatterers is dependent on spacecraft velocity. The paper also looks at the processing gain resulting from over-lapping image pixels in azimuth through the sampling of the pulse repetition frequency. Analysis of the discrete SAR model shows that when the pulse repetition frequency exceeds the antenna Doppler bandwidth by only a small margin, as is sometimes true for orbital systems, the gain is somewhat greater than that normally applied. The general approach uses end to end SAR impulse response rather than approximate extrapolation of the standard radar equation to the imaging mode. INTRODUCTION Calibration of SAR systems is increasing in importance, due to the advent of quadrature polarimetry radars (e.g., van Zyl 1990), and to more quantitatively demanding analysis of SAR data in a variety of Earth applications. Experiments based on airborne SAR systems have been concerned by variations as small as 0.01 dB as they impact the overall radiometric error budget (Kasischke and Fowler 1989), and SAR calibration results are headed below the 1 dB threshold (Gray et al. 1990). Systematic errors or biases are to be avoided. References on SAR calibration are appearing at an increasing rate, reinforced by encouraging results derived from the excellent airborne SAR systems now being oper ated by the Jet Propulsion Laboratory, the Canada Centre for Remote Sensing, and others. The growing literature is timely, given the advent of several major orbital SAR systems to operate during this decade. It is natural to expect to be able to apply the methodology developed in the SAR calibration literature to the orbital situation. By way of background, the viewing geometry normally used for analysis of SAR azimuth channel response is shown in Figure 1. Such a "flat Earth" model is quite suitable for the airborne case, from which key azimuth performance parameters may be derived. Assuming a narrow antenna pattern, the range from the radar to a scatterer is, to first order, which determines the phase, and hence Doppler, properties of the received signal as the aircraft flies past. For radar wavelength \ and antenna of beamwidth /3 and the geometric definitions implied in the figure, expressions are well known for the available integration time ß V (2) the antenna limited Doppler bandwidth It turns out that a small trap awaits those who would apply certain aircraft SAR calibration methods directly to the orbital case without accounting for the sphericity of the Earth. A systematic error can arise as a result, depending on methodology. It would seem that nowhere in the calibration literature can be found the basic concepts required. the time bandwidth product TB ajc X (3) (4)

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