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:: Relating L-band scatterometer data with soil moisture content and roughness. P. J. F. Swart

Document type:: Multivolume work

Structure type:: Chapter

185 rn ise. scan 665 with ita of both the Lai naviagion ne tagged so ìan time correc- ; and the an- :ric correction (8) itenna coordi- rmula is the : cross section ±>er to which ;ed power ^stem's inter- :he direction , For the i) a value was external cali- >een measured this function respect to the .on) . The re- i elevation ixample given iction 0 o is most accurate tin direction le last figure itenna coordi- lin function J'Jor ::: i J 3». integrated .+ 30 deg.). SCAN 665 0 = 63° Figure 4. Calculated normalized radar cross section. FIELD : Figure 6. Along-track field-averaged gamma. 4 SIR-B EXPERIMENT As already told in the introduction unfortunately the SIR-B experiment has been partly insuccesful. Orig inally, the DUTSCAT measurements should take place at 5 days within a 10 days flight scheme of the Shuttle in early September 1984. However, launching had to be delayed twice and the program reduced to 2 days, 11 and 12 October 1984. On these days the collection of ground data of the test area occured under rather wet field conditions due to extreme high precipitation in the preceding month af September. The Shuttle radar failed to produce data for our test area but scat- terometer data were gathered along with flight par ameters and video recordings. The last are meant to facilitate the interpretation of the measurements. The test area in the Flevopolder consists of large agricultural fields (75 ha). We see it in fig. 5. The lengths of the straight lines in this figure are proportional to the number of scans where the half power azimuthal antenna beamwidth is completely within the field. So field-averaging is depending upon flightparameters e.g. altitude, heading, pitch, roll, as well as incidence angle and of course fieldsize and beamwidth. With a videocamera attached to the scat- terometer antenna recordings are made containing time information from which the position of fieldboundaries in the radardata can be extracted independent of the measurement geometry. To obtain the earlier discussed accuracy of 1 dB in relation with equation (5) to (7) more than 10 scans must be available for averaging within one field. Figure 7 gives an impression of the multi-angular gamma values for the 19 different fields. We see that the data follow an S-like curve within a range of 10 dB. FIELD 1 ...19 Figure 7. Gamma versus incidence angle. The homogeneity of these fields in terms of flatness, soiltype and agricultural practise is unique. For an impression of the area the reader is referred to the literature (de Loor 1982). The flight track is located diagonally over the test area and has a length of 10 km. At the time of the measurements 19 different fields were covered. These fields were surveyed and sampled in detail which resulted in data about soil moisture, surface rough ness and vegetation (Stroosnijder 1984). The radar cross section 0 o of (vegetation covered) soils depends on a limited number of predominant surface parameters, such as those just mentioned. The relative importance of these parameters depends on radar parameters such as incidence angle, wavelength and polarization. The objective for the experiment for which data is available was to produce estimates of soil moisture and roughness by using an inverse scat tering model and field averaged O values for various incidence angles. An example of along-track field averaged a divided by the cosine of the incidence angle, or the backscat- tering coefficient y is given in fig. 6 (<0>=63 ). 5 SOIL MOISTURE AND ROUGHNESS As discussed in 2.1 the across-track ground resolution degrades for decreasing incidence angles. Because of this resolution problem we will restrict ourselves for the moment to large incidence angles. For this case the backscattering coefficient y can be written as (Attema e.a. 1982). y = F.(l-exp(-p 2 )) (g) p = 2kacos0, k=2TT/A with a the rms value of the height distribution and F an unknown intensity factor. Based on experimental evidence, especially for bare soil, it can be assumed that F is independent of incidence angle and related to the soil moisture content (Attema/Krul 1979). From eq. (9) we see that many moisture content - roughness combinations are possible at one y value and incidence angle, so that hardly any discrimination can be at tributed to one single y value. Even if a significant part of y versus incidence angle is known it might not be possible to distinguish roughness from moisture.

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