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:: Measurements of the backscatter and attenuation properties of forest stands at X-, C- and L-band. D. H. Hoekman

Document type:: Multivolume work

Structure type:: Chapter

can be used for angle discrimination within the illu minated spot. A video camera attached to the supporting struc ture of the antenna registrates the measured objects. A time indication added to the video images enables the data interpreter to link the desired objects with radar and flight data. The specifications of the DUTSCAT are listed in table 2. Table 2. Specifications of DUTSCAT (multi-band). Frequencies Antenna Transmitted power Operating range Pulse length PRF Polarization Sample frequency Range resolution 1.2, 3.2, 5.3, 9.65, 13.7 and 17.25 Ghz 0.9 m parabolic dish 250 mW 50 - 1920 meters 100 ns 78.125 kHz HH or VV 20 MHz (7.5 m), 8 bits I & Q 15 m The forest stands of interest have been measured 3 or 4 times with the DUTSCAT for each angle and/or polarization. For the relatively small stands and for the high incidence angles this repetition was found to be necessary. This can be explained as follows. The distance r between sensor and object and the ground range distance y (figure 1) will fluctuate around designed values. The effect of small roll movements and height variations of the platform can easily be quantified. Since y = h. tan (0^) h dy = d0£ + tan0- ,dh (1) cos 2 0£ This formula shows that especially at high incidence angles variations in dh en d0£ will have a strong effect. This is illustrated by the following numeri cal example: Suppose the height of flight is 200 meter and angle of incidence is 60 degrees. Realistic values for height and roll variation are dh= + 10 meter and d0^ = +2 degrees. This results in y = 346.4 meter and dy = + 48.6 meter. The variation in dy is troublesome when small stands have to be measured. If navigation is perfect, variations in height and roll angle will still cause the illuminated spot to sweep across the stand and to cross borders occasionally. Therefore only the lar gest forest stands (exceeding 200 m in ground range) have been selected for the DUTSCAT campaigns. For research the multiband scatterometer has some major advantages over the SLAR. Gamma values can be measured simultaneously in six frequencies, a choice can be made between vertical and horizontal like polarization and the system is accurately calibrated both internally and externally. The major advantage of the SLAR is its imaging capability. Spatial patterns and differences in image texture can be per ceived. Another difference between SLAR and scatterometer is not apparent immediately. It follows from diffe rences in measurement geometry. The SLAR usually is operated from larger altitudes and the across track beam width is considerably larger making the across track illuminated spot width in the order of seve ral kilometers whereas this figure is in the order of several tens of meters for the scatterometer (figure 2). As a result contributions of scatterers from different horizontal layers in the forest arrive somewhat separated in time at the receiver (section 4). This effect enables the data interpreter to distinguish sources of scattering (sections 4 and 5) but at the other hand makes 'standard' pre processing as used for non-forested areas question able (sections 4 and 6). Figure 1. Measurement geometry with height of flight (h), distance sensor - target (r), ground range dis tance (y) and angle of incidence (0f). Figure 2. The relatively small beam width and low height of flight of the scatterometer (DUTSCAT) ma kes that contributions of scatterers from different horizontal layers in the forest are measured in dif ferent range cells. For the SLAR system in x every range cell all forest layers are (equally) repre sented. 3. FOREST CANOPY ATTENUATION MEASUREMENTS USING CORNER REFLECTORS 3.1 Corner reflector experiment During the summers of 1984 and 1985 measurements of forest canopy attenuation were conducted with the use of corner reflectors. The first experiment of this kind took place at the Roggebotzand site over stands of poplar and oak with the X-band SLAR. In 1985 these measurements were continued with the X-band and the L-band scatterometer but these have not been fully analysed yet. Three corner reflectors with an 2 X-band raaar cross section (in free space) of 45 dBm

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