Remote sensing for resources development and environmental management: Remote sensing for resources development and environmental management

Damen, M. C. J.

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Multivolume work

Persistent identifier:: 856342815

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856342815

Language:: English

Additional Notes:: Volume 1-3 erschienen von 1986-1988

Editor:: Damen, M. C. J.

Document type:: Multivolume work

Volume

Persistent identifier:: 856343064

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Scope:: XV, 547 Seiten

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856343064

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(26,7,1)

Language:: English

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

Editor:: Damen, M. C. J.

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:: 2 Microwave data. Chairman: N. Lannelongue, Liaison: L. Krul

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Oil drums as resolution targets for quality control of radar survey data. B. N. Koopmans

Document type:: Multivolume work

Structure type:: Chapter

Symposium on Remote Sensing for Resources Development end Environmental Management / Enschede / August 1986 Oil drums as resolution targets for quality control of radar survey data B.N.Koopmans International Institute for Aerospace Survey and Earth Sciences (ITC), Enschede, Netherlands ABSTRACT: Spatial resolution in radar imagery is dependent on angular discrimination in along-track (azimuth) direction. Range discrimination depends on a time delay measurement, using either the duration of the pulse or a frequency-modulated pulse. To check effective spatial resolution of Synthetic Aperture Radar (SAR) or Real Aperture Radar (RAR) data, measurements can be made on the response distribution of a point target. This method, used for digital data, can assess only the peak width to the background and no effect of side—lobes or geometric distortion is taken into account. For optically correlated imagery, the method is less applicable. A pragmatic approach for control of spatial resolution is to measure the smallest distance between two point targets having approximately the same response strength, which are still visible as two objects on the image. For this purpose, a number of point targets of materials easily and cheaply available everywhere in the world (oil drums cut in half lengthwise) were used in a test site during ESA's SAR-580 experiment in Southern Spain. From their separate identification, a good deduction could be made regarding the effective spatial resolution in range and azimuth of the imagery. INTRODUCTION The SARTHI project - (a side-looking radar and IR false colour survey over the Iberian Pyrite belt (Koopmans et al. 1985) - was part of the European SAR-580 experiment carried out during 1981-84. During the radar survey flight, an experiment was carried out with drum reflectors to check the use fulness of a number of point targets to determine the spatial resolution of the radar. SPATIAL RESOLUTION The definition of spatial resolution in its simplest form is: "the minimum distance between two point- sources (objects) of equal-intensity that a sensor can record separately". The definition is not always used in this sense, however, and depending on the system, other parameters may be taken into consider ation. Forshaw et al. 1980, recognized four different types of identification of spatial resolution: 1. Geometric properties of the imaging system. 2. Ability to distinguish between point targets. 3. Ability to measure periodicity of repetitive targets. 4. Ability to measure spectral properties of small finite objects. The first type giving the geometric properties of the imaging system will be briefly mentioned here and compared with results measured according to the second type: ability to distinguish point targets. The third type, ability to measure repetive targets, deals mainly with the optical approach of defining spatial resolution in line pairs per milli-meter and will not be treated here. For side-looking radar, the spatial resolution on the basis of geometric properties in range is depen dent on the half pulse-length and the depression angle; the latter is variable over the image swath: Rgr = .. _ ^ Z cos ts where Rgr = resolution in ground range c = velocity of light t = pulse duration 3 = depression angle Here we are dealing with a range discrimination based on measurement of a time delay (duration that the pulse is emitted). To improve range resolution, the pulse may be frequency-modulated. In azimuth, the spatial resolution depends on the half-power beam-width and the range towards the object. It is an angular discrimination, hence the beam-width increases with range. The following equation is valid for a real aper ture radar: where Ra = resolution in azimuth X = wavelength Rs = slant range to target Da = diameter of aperture in wavelengt units. For a focussed synthetic aperture radar system, the azimuth is one-half of the physical length of the antenna and is independent of range distance. This is theoretical, however, and azimuth resolu tion measured according to the second type is often larger. "Spatial resolution" should not be confused with "detectability". Objects smaller than a ground resolution cell may be detectable if the small ob ject has a strong radiance or backscatter, forming sufficient contrast relative to its background. Well-known examples of such detectable objects are metal fences, corner reflectors, Lunenburger lenses, or other radar beacons. For the European SAR-580, the effective spatial resolution of the SAR imagery was measured on the basis of the response distribution of point targets (Smith, 1985) (type 4 of Forshaw's spatial resolu tion identification). Algorithms were used for digital data to select or reject a number of appro priate point targets and to calculate the average width of the response function at 3 dB below their peak value. This method assessed only the peak width of the point target to the background and no effect of antenna side-lobes or geometric distor tion was taken into account. For imagery which is not in digital form, the method is less appli cable. The results of these measurements for data corre lated at the Royal Aircraft Establishment (RAE) at 145

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