Seasat SAR Imagery Research Articles

Applicabilities of imaging radar for classification of forest vegetation

With the urgent need for experimental knowledge with imaging radar, in the last few years a great number of data sets from airborne and spaceborne systems have been collected from many European test sites. This paper reviews woodland and agricultural aspects of land use, based on the authors experience with SEASAT-SAR, SAR-580 and SIR-B imagery. It presents potential applications as well as the limitations of the microwave remote sensing sensor for operational tasks of land-use inventory.

Textural Infornation in SAR Images

A multiplicative model was used to relate the image variance for a given land-use category to the individual variances associated with image speckle and target texture. Speckle was treated as a random process governed by signal fading and was considered to be statistically independent of the textural variations associated with the spatial variations of the scattering properties of visually uniform distributed targets. Seasat SAR imagery of Oklahoma was used to evaluate the textural autocorrelation function of five land-use categories: water, forest, pasture, urban, and cultivated. It was found that the maximum classification accuracy achievable using first-order statistics was 72 percent and that this level of accuracy was obtainable only by significantly degrading the spatial resolution in order to increase the number of independent samples per pixel. In contrast, second-order statistics-specifically, image contrast and inverse moment-provided a classification accuracy of 88 percent, with only a modest degradation in spatial resolution. A second study using SIR-A imagery of five forested regions has shown that the use of textural information can improve the classification accuracy among the five forest types from 75 to 93 percent.

Use of SEASAT SAR imagery for geological mapping in a volcanic terrain: Askja Caldera, Iceland

Abstract Nine distinct surface types have been identified by comparison of SEASAT SAR imagery with field observations in the Askja Caldera region of central Iceland. A map of radargeological surface type is presented, together with field descriptions and discussion of the influence of the surface types on radar signal return. Surface relief, surface roughness and clast size were found to have the greatest importance for imageinterpretation.

Utilization of Spaceborne SAR Data for Mapping

Recent developments in automated processing of digital SEASAT SAR imagery have made feasible the generation of large-scale high-resolution maps. Standard preprocessing of raw data into digital images results in geometrically distorted imagery. Computer algorithms have been developed for unsupervised pixel location, geometric rectification, and mosaicking of multiple-image frames without ground control points. These algorithms utilize knowledge of the spacecraft trajectory data, the imaging geometry, and the coherent properties of the sensor to generate the required processing parameters. This paper discusses the advantages as well as the inherent limitations of this technique, analyzes the associated errors, and presents results using SEASAT SAR imagery. Also discussed are the results of the recent shuttle imaging radar (SIR-A) experiment as well as a follow-on experiment (SIR-B) planned for 1984.

Radargeologic interpretation of Seasat imagery of Iceland

Abstract A geologic interpretation of a 1:500 000 scale mosaic of optically correlated Seasat SAR imagery showed that 14 of the 17 major units mapped by the Geological Survey of Iceland could be recognized although it was not possible to close all the radar geologic boundaries. Interactive work with computer correlated imagery produced no additional information significant to mapping at that scale. Comparison with Landsat revealed that the radar produced more data on ice type, alluvial categories and upon lineaments but the overall interpretative value of Landsat was clearly the better of the two. The results of local co-registering Landsat and Seasat were interesting but did not cause any modification of the regional interpretation

BOOK REVIEWS

Book Reviewed in this article:RECTIFIED PHOTOGRAPHY. By R. W. A. Dallas.THE STEREO VIEWER. By F. Vögtle.GROUND AND AIR SURVEY FOR FIELD SCIENTISTS. By J. Wright.THE AEROFILMS BOOK OF BRITAIN FROM THE AIR. By B. Stonehouse.AERIAL ARCHAEOLOGY. Volume 6. 1980. Editor D. A. Edwards.AUGMENTATION OF LANDSAT MSS DATA BY SEASAT SAR IMAGERY FOR AGRICULTURAL INVENTORIES. By D. R. Nüesch.

A Review of: “Augmentation of Landsat MSS Data by Seasat SAR Imagery for Agricultural Inventories.” By D. R. NÜESCH. (Zürich: University of Zürich, Remote Sensing Series, Vol. 7, 1982. [Pp. 106,] Price SFr. 30.00 (paperback).

(1983). A Review of: “Augmentation of Landsat MSS Data by Seasat SAR Imagery for Agricultural Inventories.” By D. R. NUESCH. (Zurich: University of Zurich, Remote Sensing Series, Vol. 7, 1982. [Pp. 106,] Price SFr. 30.00 (paperback). International Journal of Remote Sensing: Vol. 4, No. 2, pp. 479-479.

An evaluation of seasat SAR imagery for urban analysis

Digitally processed Seasat SAR imagery of the Denver, Colorado, area is analyzed with regard to the types of urban data that can be detected and/or inferred from satellite-borne L-band systems. Black-and-white images of the scene were generated at three scales to determine the advantages and detail discernible at each level of display. The large-scale imagery was density-sliced to evaluate the feasibility of producing a semiautomated land-cover classification from the SAR data. Gray level classes were assigned colors to aid interpretation and subsequently compared with the black-and-white images to assess the contribution of each technique and benefits of combining the data from both procedures.

Location of Spaceborne Sar Imagery

A method has been developed to determine the location of a pixel in a digital SAR image. This technique utilizes the spacecraft ephemeris data and the characteristics of the SAR data collection system to produce an estimate of the latitude and longitude of an arbitrary pixel. This approach has an advantage over previous techniques in that it requires no reference points and is independent of spacecraft attitude knowledge or control. Tests were conducted using SEASAT SAR imagery, comparing predicted feature location with the location as determined by high precision area maps. Results indicate an accuracy of 200 m is attainable with this method. Error sources are analyzed and recommendations are given to improve image location accuracy in future spaceborne SAR's.

Use of elevation models for landform analysis by SEASAT-SAR imagery

Within the framework of a long-term project aimed at the development of methods and techniques for regional land evaluation and land-use planning, an attempt has been made to assess the potential of SAR imagery as a source of information regarding landform characteristics which are directly or indirectly related to slope instability. In fact, geomorphic features, such as elevation, slope angle, local relief and drainage network, strongly control radar signature. Hence the feasibility of applying radar imagery to qualitatively and quantitatively detect and classify landslide and erosional phenomena. However, in hilly and mountainous areas very large geometrical and radiometrical distortions hamper to a great extent the interpretation of SAR data. Therefore, the development of efficient and suitable techniques is necessary for the correction of lay-over and shadowing, mainly due to local relief and ground slope. A numerical procedure has been implemented using both SEASAT-SAR data and a digital terrain model of a sample area, the Buonamico basin, Aspromonte, Southern Italy. Geometrical operators and interpolation functions have been employed in order to resample radar pixels into a new, topographically referenced, network. In addition, simple models have been applied to accomplish empirical radiometrical calibrations. As a result, some geomorphic features associated with slope instability phenomena have been detected.

The observation of tidal patterns, currents, and bathymetry with SLAR imagery of the sea

Work done until 1978 on the visualization of currents, bathymetry, internal waves, etc., in SLAR imagery of the sea is reported. It did not receive much attention until the SEASAT SAR imagery showed these effects on a global scale. Although we know, qualitatively, how these images come about we are yet far from knowing how to extract more quantitative data from them on depth, current speed, etc. Much research effort is still needed here and for this work a simple real-aperture SLAR can be a very useful tool.

Seasat Orbital Radar Imagery for Geologic Mapping: Tennessee-Kentucky-Virginia

The purpose of the reported study is to analyze Seasat SAR imagery of a heavily vegetated mountainous land surface and to determine the potential of this microwave imaging system for geologic mapping. It is found that geologic mapping using orbital Seasat SAR imagery is feasible in the Appalachian Valley and Ridge province, where the radar system is highly sensitive to change of surface slope. Image tones and textures correlate with distinctive topography, from which generalized lithologic and structural interpretations are derived. Major and minor linear topographic features are easily mapped from the SAR images. The SAR sensor suppresses subdued geomorphic lineaments that strike parallel with or near to the radar look direction. This deficiency is partly compensated by the dual directions of radar illumination obtainable from the Seasat imaging system.