×

You are using an outdated browser that does not fully support the intranda viewer.
As a result, some pages may not be displayed correctly.

We recommend you use one of the following browsers:

Full text

Title
Proceedings of the Symposium on Global and Environmental Monitoring

3.3 Optical measurements
The effects of intnsic parameter of the soil surface (here
soil moisture) observed under varying extrinsic
conditions of measurement (spectral band, angle of
incidence, solar illumination angle) are to be
discriminated in order to establish the most sensitive
and optimal conditions to detect soil surface changes
due to slaking.
Whatever the configuration of the instrument, it is
clear, as shown in Figure 5, that the wet condition of
soil moisture is not appropriated to discriminate stages
of slaking. Soil moisture decreases reflectance level. Wet
condition produce unsensitive and quite constant
measurements. In dry condition, the reflectance globally
increases with the stage of slaking as the Tortuosity
index decreases.
The effect of the solar illumination angle is shown in
Figure 6. Whatever the spectral bands, it affects the
reflectance level. At 6.00 am or 6.00 pm, the presence
of shadows decreases the reflectance level. But it does
not seem to affect the spectral discrimination of stage of
slaking although some obtained experimental
relationships are not continuously decreasing.
Nevertheless, the most satisfactory relationships are
obtained at midday whatever the spectral band and the
XS3 band seems to be more interesting to detect
changes in stage of slaking.
The reflectance level is also affected by the chosen angle
of incidence (0* or 23*). But, the relationships obtained
at 23 s exhibit quite similar behaviors which do not
modify conclusions discussed previously.
4. CONCLUSIONS
We have observed in controlled conditions that it is
possible to discriminate stage of slaking on the based of
multitemporal remote sensed data.
For practical purposes, the possibility of slaking survey
using active microwave remote sensing is heavily
improbable. It is limited to a narrow configuration of
the instrument only compatible with the use of an
airborne system which will necessary have a limited
spatial resolution. Thus, the greatest penetration depth
of microwave renders the discrimination of slaking more
dependent on soil moisture conditions in the near
surface soil layers.
Optical remote sensing technique seems to be more
promising. Nevertheless, further studies will be
necessary to study the effect of the initial soil roughness
condition. The new measuring programs will also
include various azimuthal viewing angles for the optical
measurements. These studies will provide useful
informations to be incorporated for the explanations of
multitemporal SPOT images in order to assess soil
erosion inventories.
5 REFERENCES
Bertuzzi P., Bruckler. L., Gabilly, Y. and Gaudu, J.C.,
1987. Calibration, field testing and error analysys of a
gamma-ray probe for in situ measurement of dry bulk
density, Soil Science, 144(6): 425-436.
Bertuzzi, P., Caussignac, J.M., Stengel, P., Morel, G.,
Lorendeau, J.Y., and Pelloux, G., 1990a. An automated
non contact Laser profile meter for measuring soil
roughness in situ. Soil Science 149(3), in press, 8pp.
Bertuzzi, P., Rauws, G. and Courault, D., 1990b.
Testing roughness indices to estimate soil roughness
changes due to simulated rainfall. Soil k Till., in press,
13 pp
Boiffin, J., 1984. La degradation structurale des couches
superficielles sous l'action des pluies. Thèse de
Docteur-Ingénieur, Inst. Nat. Agron., Paris, 128 pp.
Boiffin, J., 1986. Stages and time - dependency of soil
crusting in situ. In: Assessment of soil surface sealing
and crusting, Callebaut, F.; Gabriels, D. and De Boodt,
M. (Editors), Flanders Research Center for Soil Erosion
and Soil Conservation, Ghent, 91-98.
Cierniewski, J., 1987. A model for soil surface roughness
influence on the spectral response of bare soil in the
visible and near infrared range. Remote sensing of
environment, 115: 23-97.
Curran, P.J., Foody, G.M., Kondratyev, K.Ya.,
Kozoderov, V.V. and Fedchenko, PP., 1990.
Reflectance of soil in the laboratory and field. In
Remote Sensing of soil and vegetation in the USSR,
edited by Taylor k Francis Ltd, London, Great Britain,
pp 63-82.
Guyot, G., Hannocq, J. F., Saint, G. and Buis, J. P.,
(1984). Mise au point d'un radiomètre de simulation
SPOT, m Proceedings of 2 nd Int. Coll, on Spectral
Signatures of Objects in Remote Sensing, held in
Bordeaux, France, 12-16 Septembre 1983, edited by
"Les colloques de l'INRA", INRA Publications, Pans,
France, 23: 153-157.
Ulaby, F.T., Batlivala, P.P. and Dobson, M.C., 1978.
Microwave backscatter dependence on surface
roughness, soil moisture and soil texture. IEEE Trans.
Geos. Rem. Sens., 16: 286-295.
Ulaby, F.T., Moore, R.K. and FUNG, A., 1982.
Physical mechanisms and empirical models for
scattering and emission. In Microwave remote sensing,
Active and Passive, Volume II edited by
Addison-Wesley Publishing Company, Reading,
Massachusetts, USA, pp 816-921.
Van der Heide, G. and Koolen, A.J., 1980. Soil surface
albedo and multispectral reflectance of short-wave
radiation as a function of degree of soil slaking. Neth. J.
Agric. Sci., 28: 252-258.
119