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

Damen, M. C. J.

Bibliographic data

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:: 3 Spectral signatures of objects. Chairman: G. Guyot, Liaison: N. J. J. Bunnik

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Multitemporal analysis of Thematic Mapper data for soil survey in Southern Tunisia. G. F. Epema

Document type:: Multivolume work

Structure type:: Chapter

valid for reflectance values of A above 0 %. The first example is not valid if A is not equal to 0 %. In that case the reflectance of A in that band has to be subtracted from all other points before a constant ratio will give an equal decrease. Table 2. Examples to show difference between ratio and difference image. before change after change sur face nr. cover refi. (%) cover refi (%) . ratio abs. decrease 1 100%A 0 100%A 0 X X 2 100%B 20 50%A,50%B 10 .5 10 3 100%C 40 50%A,50%C 20 .5 20 1 100% A 0 100% A 0 X X 2 50%A,50%C 20 100%A 0 0 20 3 100%C 40 50%A,50%C 20 .5 20 Field measurements of reflectance have been performed in the month before the acquisition of the May image. The values found with the reflectometer cannot be compared directly with the TM data due to the type of apparatus (Epema in prep.), and the fact that there is a difference between reflectance at the top of the atmosphere and at the surface. In table 3 normal reflectance values are given for a range of surfaces. Table 3. Representative normal reflectance values of May 1985 with solar zenith angle of 20 degrees. green red nir Playa and playa border sealed surface 22.2 22.6 23.5 thin salt layer 25.2 28.0 29.4 extremely dry 30.4 34.7 39.1 extremely wet 14.9 17.1 17.2 extr dry near oasis 33.2 38.2 43.7 Footslope sealed surface 39.4 41.5 48.7 gypsiferous sand 47.6 51.1 57.9 lygeum spartum 14.4 14.5 19.0 Interpretations based on the above described images are complementary to each other. In order to observe variations within the playa difference images will be most useful. The influence of vegetation or shadow can be found at their best on ratio images. In principle for vegetation from all values first the reflectance of vegetation has to be subtracted before the ratio is calculated. The same will hold for the shadow influence at short wavelength. A generalized map of part of the area, subtracted from different images and multitemporal plots of bands and band ratios, is given in fig. 2. In general one may observe an absolute increase in reflectance for most of the playa and playa border zone. This will be due to the presence of salt at the surface. The increase in salt cover will remain important for a long period after rain storms, while the effect of increasing moisture content will last only for a short time. The decrease in reflectance for a part of the playa border zone north of the oasis is due to the effect that the surface is after the rainstorm comparable with the rest of the playa border zone. Probably in January surfaces as described in table 4 dominated. Only a small part of the playa remains without changes. bands code 1 4 7 1 0 0 0 0 = Oasis 2 0 +2 0 Pl= Playa and playa border 3 0 0 -1 Fs= Footslope 4 +2 +2 +1 5 +2 +1 0 0 = no or very weak change 6 mix 3/5 1 = weak change 7 -3 -3 -1 2 = moderate change 3 = strong change + = refl. May > January refl. May < January Fig. 2. Most important changes in reflectance for part of the study area. In the footslope area for most surfaces reflectance remains about the same. For several units with still a high reflectance in band 7 (low cover of gypsum crust or gypsum sand) a small absolute decrease in reflectance occurs in May. The same may be true for other parts of the footslopes, but in this area the variance within the units is higher than the possible change. The change may be due to the effect of exposure differences and related amount of shadow. Also for some other parts with a certain slope the effect is present. However no direct model can be developed, as in the correction procedure reference objects are used in stead of an atmospheric model. Another phenomenon which can be observed is the effect of increase in vegetation for a part of the footslope. This relative increase in band 4 for May in comparison with January will be caused by vegetation which is present all over the year. If this vegetation is healthy, the reflectance increases in band 4 and remains about the same in other bands. In other parts of the footslope area permanent vegetation made up only a small part of the surface. It has been observed that annuals between this permanent hummocks make no more than about 2 % of the surface. The effect of this vegetation is a decrease in reflectance in all bands (hardly less for band 4). The cause that this cannot be read from the data is the small influence on reflectance in comparison with the reflectance as a whole. Since one of the completely bare units in the playa reacts in all bands, within the limits of significancy, the same as the selected reference object, it can be concluded that the influence of vegetation is small for the selected reference object. The most important changes in reflectance are due to salt efflorescence, vegetation development and exposition. However also other differences between the images exist or may exist. Over a very small part of the study area wet surfaces are present in May. The change in reflectance in the eastern part

Access restriction

Copyright

fullscreen: Remote sensing for resources development and environmental management (Volume 1)

Multivolume work

Volume

Chapter

Chapter

Table of contents

Cite and reuse

Volume

Chapter

Image

Image fragment

Citation links

Citation recommendation