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:: 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

246 From the plot of near infrared to red (Thematic Mapper band 4 to 3; wavelength respectively 776 to 905 nm and 624 to 693 nm) it can be concluded that most units with the exception of a small group show spectral curves representative for soils with a low to absent vegetation cover. Comparing feature space plots of the first four bands (band 1 452-518 nm and band 2 529 to 610 nm) in the visible and near infrared part, three main types can be discriminated: 1. a small group with vegetation (palm trees in the oasis) with a low reflectance for blue, green and red and intermediate reflectance in the near infrared and a high 4/3 ratio. 2. a group of (almost) bare soils changing to a range of intermediate to very low reflectance values in band 4. 3. a group of bare soils, having an intermediate to very high reflectance in all 4 bands. Introducing also band 7 (2097 to 2347 nm) the above mentioned groups can be characterised as follows: 1. the reflectance of the oasis is very low in band 7, as can be expected for vegetation. 2. this group has like in band 4 an intermediate to very low reflectance. 3. two extremes develop within this group: 1. one extreme has both in band 7 and in band 4 the intermediate to very high reflectance. 2. the other extreme has in band 7 low values in stead of intermediate values and intermediate values in stead of very high values. Band 5 (1568 to 1784 nm) can be considered as in termediate between the first four bands and band 7. The following characteristics can be given of the 3 groups. The oases, covered with palm trees in the upper layer, are group 1. Group 2 consists out of units of different parts of the playa and playa border zone. The relatively dry footslope and dune areas are the third group. The large decrease of reflectance in band 7 in 3.2 is due to the presence of gypsiferous sand or gypsum crust at the surface. Differences in reflectance within the footslope and playa group are due to different amounts of stones, crust, gypsiferous or non-gypsiferous sand, vegetation, surface roughness, exposition, moisture, salt content and mineralogy of the top surface. 3. CAUSES OF DIFFERENCE BETWEEN JANUARY AND MAY DATA The differences between the two days can be divided into differences of the surface itself and those due to the effect of sun elevation at Landsat overpasstime and turbidity of the atmosphere. 3.1 Difference of the surface The most probable differences of the surface may be caused by the effect of rain, wind and vegetation. Due to the effect of rain the surface layer may be moist. An increase in moisture content in the surface layer leads to a decrease in reflectance. The cause and relation between reflectance and moisture content are described a.o. by Angstrom (1925), Bowers and Hanks (1965) and Planet (1970). The decrease in reflectance will last for a longer time if the groundwater table is close to the surface. Therefore, if the moisture effect of rain is visible; this will be in the playa and playa border zone. Field measurements showed that this moisture effect in the top surface layer has disappeared in the footslope area within a day. A second effect of rainfall is the redistribution of £>alt. Salt efflorescence occurs in the playa and playa border zone. It was observed in May 1985 that even in the relatively high parts of the playa border zone (up to 1 meter) this phenomenon occured and lasted at least for a week after rainfall. A third effect to be mentioned is the occurence of slaking after rainfall. This effect is also important in the relatively dry areas even in the dunes and may last for long periods. Erosion and sedimentation is a fourth possibility, which may affect reflectance if rainfall occurs. Due to the wind in sand areas the roughness of the surface may change as a function of the windvelocity before and at the time of Landsat overpass. Moreover dunes may migrate. Since sand grains or sheets are often an important part of the surface, the effect on reflectance may be present. The vegetation in May in this area will in general be more green and healthy than in January. Moreover annuals may be present on places, where in January no plants are present. In order to estimate the effect of vegetation the spectral reflectance curves in relation with the soil surface have to be taken into account. All effects mentioned above may differ in place not only due to the characteristics of the surface but also due to irregular distribution of rain, runoff and wind within the area. 3.2 Other differences The solar zenith angle at the acquisition dates differs significantly (29 degrees in May and 60 degrees in January). Moreover differences in turbidity of the atmosphere at the two days may exist. The turbidity and solar zenith angle influence the relation between reflectance at the top of the atmosphere and the surface reflectance. Different approaches and formulas relating these two types of reflectance can be found (Otterman and Fraser 1976, Nack and Curran 1978, Chen and Ohring 1984, Koepke et al 1985). The relationship between surface albedo (a ) and planetary albedo (ax; albedo at the top of the atmosphere) can^ be approximated according to Koepke et al (1985) by: a=a+ba (1) where a^= path raâiance b = two way transmittance A nomogram is presented by Koepke et al (1985) to find values for a and b at different solar zenith angles and turbidity factors. In table 1 a and b values are presented for 29 and 60 degrees solar zenith angles with albedo expressed in reflectance percentage. As can be expected path radiance will increase with increasing solar zenith angle and tubidity of the atmosphere, while the two-way transmittance will decrease with these two factors. It may be clear that transmittance is wavelength dependent. Hence the correction for albedo bands cannot be applied directly on the different bands. Table 1. Path radiance (a) and two-way transmittance (b) values for different turbidity factors (T at 550 nm) and solar zenith angles of 29 and 60 degrees (after nomogram presented by Koepke et al. 1985). zenith angle 29° 60° a b a b 3.5 .79 5.7 .73 3.6 .77 5.9 .71 5.7 .62 10.3 .53 A soil Therefor function direct (Makarov 1981). (1977) reflecta converte implies zenith i natural surface would gi sun dep degrees probably waveleng With 1 shadow v areas w: higher a will lea will be solar ze January, will re. Finally parts oi function time of 4. C0NVE The ref] the atmc shown, t at the waveleng even in correcte for both Since calculat These mi lower li are equa the feat is the constant All ap - Upper necessar: lower or due to 1 surfaces advantagi that t minimize* - The as space ma; - Ref lei constant In ord ref lectai comparab' Ultimai which a this wii; the foot been se reflectai this obj bare pla; way in a approach May have 0.882 an with Ja

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