Remote sensing of the Earth with spaceborne imaging radars

Spaceborne imaging sensors in the visible, infrared and passive microwave have been used to observe and study the Earth's surface since the early stages of the space program. More recently, active microwave imaging sensors (radars) have been developed to extend our capability to study the Earth surface processes. Imaging radars, flown on Seasat (1978) and the Shuttle (1981, 1984), acquired synoptic images of a variety of geologic, biologic, and oceanographic features and provided new insight in some of the land and ocean processes. Subsurface synoptic imaging was achieved for the first time in some of the arid regions of the world. Soil moisture distribution after a rainstorm was clearly delineated, opening the possibility of its monitoring on a global basis. Polar ice distribution and dynamics over large areas in the Beaufort Sea were monitored over a three-month period, thus allowing the possibility of operational observation of ice dynamics in support of polar navigation. The successful development and flight of these spaceborne imaging radars was the result of major technological developments in the 1970s. They used some of the largest spaceborne lightweight planar array antennas (2X10 m) with printed radiating elements. The transmitters were fully solid state and generated a 1 kw peak power signal at L-band (1.2 Ghz). The processing of the received data to generate the high-resolution (25 to 40 m) imagery was done using both optical and digital processors. More advanced imaging radar systems are under development. Multispectral, multipolarization imaging radar systems are under development for flight in the late 1980s, thus extending our capability of detailed studies of the Earth surface processes and the nature of its cover. Extremely fast SAR digital processors are under development using the most advanced integrated circuits and allowing real-time processing of the data. This corresponds to a computational capability of 6 X 10^9 operations/s. This chapter consists of a review of the recent scientific and technological developments in the field of Earth observation with spaceborne imaging radars and an overview of planned activities in the 1980s

Shuttle Active-Microwave Experiments (SAMEX) program

The Shuttle active microwave experiments (SAMEX) program is reviewed. The key implementation aspects are presented

The Second Spaceborne Imaging Radar Symposium

Summaries of the papers presented at the Second Spaceborne Imaging Radar Symposium are presented. The purpose of the symposium was to present an overwiew of recent developments in the different scientific and technological fields related to spaceborne imaging radars and to present future international plans

Spaceborne Imaging Radar Symposium

An overview of the present state of the art in the different scientific and technological fields related to spaceborne imaging radars was presented. The data acquired with the SEASAT SAR (1978) and Shuttle Imaging Radar, SIR-A (1981) clearly demonstrated the important emphasis in the 80's is going to be on in-depth research investigations conducted with the more flexible and sophisticated SIR series instruments and on long term monitoring of geophysical phenomena conducted from free-flying platforms such as ERS-1 and RADARSAT

Proceedings of the Third Spaceborne Imaging Radar Symposium

This publication contains summaries of the papers presented at the Third Spaceborne Imaging Radar Symposium held at the Jet Propulsion Laboratory (JPL), California Institute of Technology, in Pasadena, California, on 18-21 Jan. 1993. The purpose of the symposium was to present an overview of recent developments in the different scientific and technological fields related to spaceborne imaging radars and to present future international plans. This symposium is the third in a series of 'Spaceborne Imaging Radar' symposia held at JPL. The first symposium was held in Jan. 1983 and the second in 1986

Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology

In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data

Multipass SAR interferometry. A tool for geologic analysis

This paper investigates how the information content of repeat pass satellite SAR interferometric (INSAR) data can be used to provide the geologist with a tool which can improve his ability and efficacy in the geologic analysis of SAR imagery. INSAR processing produces interferometric fringes, coherence and amplitude images. To produce an interferometric DEM phase unwrapping is a critical step. For phase unwrapping, we propose the WLMS (Weighted Least Mean Square) estimation of the phase, which is a generalization of the least-mean square method. The crucial step in WLMS approach is the weighting procedure. We propose a weighting algorithm based on the fusion of a priori information extracted from different interferometric products. These different information channels—DEM, amplitude and coherence—can be effectively fused to convey information to the geologic interpreter using 3D stereoscopic visualization;SAR stereo pairs were artificially generated using the interferometric DEM and the intensity image or the coherence image of the area overlaid. In order to ascertain the performance of the procedure a number of tests were carried out over various sites in Matese (Southern Italy), which has a fairly demanding topography, using ERS SAR tandem data. The results demonstrate that WLMS unwrapping method is sufficiently robust in capturing the morphology of the area and that stereoscopic visualization greatly facilitates geologic interpretation and the observation of detailed features of the terrain

PROCESSING OF SLAR IMAGES

An X-band Side Looking Airborne Radar (SLAR) has been developed and constructed. The recorded raw images had to be corrected both radiometrically and geometrically. To achieve this goal, different digital image processing methods have been applied. The obtained results are images fitting well to the original maps of the landscapes. Final resolution of the corrected images is 10 ... 15 m

SAR interferometric coherence in wide band systems

This paper presents a study of the interferometric coherence aimed to the understanding of the main sources of phase error of an operative wide band system. This objective is accomplished by finding a theoretical expression of coherence based on a suitable model capable of including the roughness of the surface, which produces decorrelation besides the conventional spectral overlapping approach. The analysis is validated by means of numerical simulations and controlled experiments in anechoic chamber, with the aim of extrapolating the obtained results to airborne and spaceborne imaging radars.Peer Reviewe

Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology

In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data