Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

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

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

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:: [TP-4 SOILS]

Document type:: Multivolume work

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Chapter

Title:: REFLECTANCE IN SPOT BANDS AND MICROWAVE BACKSCATTERING COEFFICIENT IN C BAND AS A FUNCTION OF STAGE OF SLAKING OF BARE SOIL. Patrick BERTUZZI,Dominique COURAULT, Gérard GUYOT and Emile CHAPUIS

Document type:: Multivolume work

Structure type:: Chapter

second one is the Tortuosity index (T) which is defined by the ratio : L -Lo T = Lo where L is the actual length of the profile and Lq is the projected horizontal length of the profile. One major interest of the tortuosity index is related to its smaller sensitivity to field variability compared to other roughness indices (Bertuzzi et al., 1990b). Soil surface changes resulting from the sealing processes was evaluated on three localized 1 m 2 surfaces of reference using the method proposed by Boiffin (1984, 1986). According to visual cntera, the evolution of the soil surface structure during slaking can be classified in five typical stages. (1) So, initial soii surface resulting from tillage. (2) Si strutural crust. Soil aggregates and clods disintegrate due to raindrop impacts.Continuous patches appear and expand due to interstitial infilling. (3) S\ + local appearance of depositional crusts. (4) S2 depositional crust; the fragmented layer becomes continuous; depositional areas are formed in small surface depressions where puddles appear during rainfall (5) SU the soil surface appears to be completely close and continuous. 3. RESULTS AND DISCUSSIONS 3.1 Ground measurements Mean values of soil volumetric water content were estimated from the 10 samples. They were plotted against the degree of slaking in Figure 3. The vertical bar corresponds to + /- standard deviation of the 10 samples. In wet condition, soil draining contributes to decrease soil moisture very quickly during the diurnal phase of the day. Dry condition corresponded to mean water contents less than 0.19 cm +3 .cm' 3 . This limited value may appear high. They must analysed in the context of the chosen sampling procedure. Whatever the spectral bands, it is not possible to attribute a real physical sense to calculated soil moisture. If fact, soil moisture gradients are generally very high in the top soil layers particularly in dry conditions. The sampling depth averaged the effect of water gradients. For optical measurements, dry conditions always corresponded to uniform and light soil surface. Table 2 shows the decrease of the two roughness indices as functions of the cumulative rainfall and the stage of slaking. These are mean values computed from the results of the twelve sampled roughness profiles. 3 2 Microwave measurements In Figure 4, the backscattering coefficient is plotted against the Tortuosity index. The vertical bar displays the magnitude of the three backscatter measurements obtained during the diurnal phase of the day for each soil moisture condition and the corresponded stage of slaking. Whatever the angle of incidence, a change in soil moisture conditions increases the curve level and Figure 3 : Mean volumetric water content as a function of the stage of slaking. Table 2. Mean roughness indices as functions of cumulative rainfall and the stage of slaking. Stage Rain (mm) s (m) T So 0 0.013 1.79 Si 30 0.012 1.60 su 64 0.010 1.38 S2 100 0.009 1.20 S 2 + 124 0.009 1.18 influences the variability of the backscatter measurements. It is always smaller in wet condition although the volumetric water content decreases rapidly ( Figure 3) At 50° of angle of incidence, the backscattering coefficient, exhibits a small increase with the Tortuosity index. But, the sensitivity of the backscattering coefficient is the order of magnitude of the observed variability. At nadir (0°), the backscattering coefficient is more sensitive to roughness changes due to slaking whatever the soil moisture conditions. In term of the standard deviation of height (s), the decrease of surface roughness (about 4 mm) due to slaking may appear very small. Consequently, only backscattering measurements of the coherent component obtained in the specular direction are sufficiently sensitive to detect roughness changes due to slaking. This will be probably verified whatever the initial roughness conditions. 117

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