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

non occured if all. a occurence t is also *ven in the a fourth jctance if aughness of on of the of Landsat Since sand part of the . present, a will in in January, s, where in to estimate reflectance have to be ar in place the surface n of rain, tion dates iay and 60 ¡rences in o days may lith angle nee at the lectance. iting these tterman and and Ohring hip between bedo (ax; e) can* 3 be 985) by: 1 (1985) to olar zenith 1 a and b grees solar reflectance diance will angle and he two-way wo factors. wavelength Lbedo bands ant bands. id two-way L turbidity ingles of 29 d by Koepke A soil surface is an imperfect diffuse reflector. Therefore the reflection behaviour will be a function of relative magnitude of diffuse and direct radiation and of solar zenith angle (Makarova et al (1973), after Kondratyev et al 1981). Bartman (1980) and Larson and Barkstrom (1977) established maps in which the surface reflectance at a certain solar zenith angle is converted to standard reflectance. This formula implies a relatively large influence of solar zenith angle due to the non diffuse behaviour of natural surfaces. Applying this formula a standard surface reflectance of for instance 20.0 percent would give for a solzr zenith angle of 60 degrees a sun dependent reflectance of 22.0 and for 29 degrees of 16.3 percent. These formulas are probably dependent of the type of surface and wavelength. With increasing solar zenith angle the amount of shadow will increase especially in rough areas and areas with a high drainage density. Although an higher amount of shadow at a certain sun elevation, will lead to a decrease in reflectance this effect will be counteracted by the difference between the solar zenith angle dependent reflectance of May and January. Sloping areas with various expositions will react different from relatively flat areas. Finally it must be noted that the reflectance of parts of the playa with hygroscopic salts are a function of the time of the day and hence of the time of Landsat overpass. 4. CONVERSION OF JANUARY AND MAY DATA The reflectance values calculated for the top of the atmosphere cannot be compared directly. As is shown, these values can be converted to reflectance at the surface, if turbidity, as a function of wavelength and solar zenith angle, are known. But even in that case, reflectance values have to be corrected for sun elevation to get comparable data for both days. Since there is much uncertainty in these calculations other approaches are to be followed. These may be the assumption that the upper and lower limits or the PI and P99 of both data sets are equal. It can also be assumed that the shape of the feature space plots are comparable. Another way is the selection of reference surfaces which are constant for both days. All approaches have disadvantages: - Upper and lower limits for both dates are not necessarily the same. One of the days may have lower or higher reflectance values, for instance due to the fact that very wet surfaces or sealed surfaces are present in May or January. The advantage of using PI and P99 is laid in the fact that the influence of misregistrations is minimized. - The assumption of similar shapes of the feature space may be wrong. - Reflectance of reference objects may not be constant. In order to compare the results of calculations, reflectance values of May are converted in values comparable with the January data. Ultimately that approach has been adopted in which a reference object has been chosen, since this will give the most reliable results. A part of the footslope area with low relief intensity has been selected. There may be some changes in reflectance due to the influence of vegetation of this object. The fact that parts of the complete bare playa however have to be corrected in the same way in all bands leads to the assumption that this approach is still not too bad. Bands 1, 4 and 7 of May have to be multiplied by respectively 0.919, 0.882 and 0.913 in order to get values comparable with January reflectance at the top of the 5. RESULTS AND INTERPRETATION The reflectance values of May and January are made comparable with the aid of a reference surface. Apart from this radiometric transformation also geometrically the May image was converted with the January data with the aid of ground control points. A first order transformation has been applied, which gave an estimated standard error of less than a pixel in both directions according to the statistical analysis. In this way both the location and the reflectance values are comparable now. In order to study the changes a large range of images and plots can be made. The construction and interpretation of 1, 4, 7 combinations of both data, with a linear stretch between the same limits, is a good first approach. A compariéon of both images will give a good overview of spatial dynamics. It is also possible to make multitemporal combinations or perform division or subtraction of bands of the two days after the geometrical and radiometrical corrections. Three types of multitemporal images can be discriminated: a colour combination, a ratio and a difference product. Again the use of band 1, 4 and 7 is most promising. - colour combinations Useful products are combinations in which a primary colour is assigned to one day and a secondary colour to the other day. An example is a combination of band 1 of May in red and band 1 of January in cyan. If no changes occur, the grey tones represent the relative reflectance. - ratio A division of one band in May (corrected) by the same band in January will give a ratio of 1 for pixels with unchanged reflectance, above 1 for pixels with a relatively high reflectance in May and below 1 for a high January value of reflectance. Lines with a constant ratio in plots connect points with the same relative decrease or increase in reflectance. - difference An image made by subtraction of January from May (corrected) would also give a value of 1 in the case of no change, above 1 for a relatively high reflectance in May, and below 1 for a low May reflectance. Still there is an important difference between the ratio and difference image. In this latter image the same value will be found for all points with the same absolute decrease or increase in reflectance. The choice out of the two latter products will depend on the type and cause of change. For a simplified hypothetical example the difference will be explained (table 2). Assume the reflectance of surface 1 to be 0 % and the reflectacne of two surfaces with a different mineralogical composition respectively 20 % and 40 %. If due to a special event, surface 2 and 3 changes in such a way that both surfaces are covered for 50 % with surface cover type A, the reflectance will change to respectively 10 % and 20 %. A ratio image will give in this case the same value for this identical change. A comparable example will be given for the difference image. Again the reflectance of the three surfaces are respectively 0 %, 20 % and 40 %. However the reflectance of surface 2 is now made up for 50 % of surface cover A and 50 % of surface B. If the amount of cover with A increases for both surface 2 and 3 with 50 % the reflectance will change respectively to 0 % and 20 %. A difference image will give now the same value for this identical change. The second hypothetical example is also

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