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:: 856641294

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Scope:: IX Seiten, Seiten 551-956

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A,. A. Balkema

Identifier (digital):: 856641294

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(26,7,2)

Language:: English

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

Editor:: Damen, M. C. J.

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:: 6 Hydrology: Surface water, oceanography, coastal zone, ice and snow. Chairman: K. A. Ulbricht, Co-chairman: Mikio Takagi, Liaison: R. Spanhoff

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Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Shape and variability of the absorption spectrum of aquatic humus. H. Buiteveld & F. de Jong, R. Spanhoff, M. Donze

Document type:: Multivolume work

Structure type:: Chapter

i1—25 November ,, 1984, etation of the northern >82". JRC Report , 1983, it 4 i northern ral Signatures ir 1983, iscence ig 'Gelbstoff' submitted to , S.,A., 1984, nguela ebruary 1980." eport on in some ing group A 19620. hop on remote orthern t JRC Ispra. 85.03 (1985). n of satellite the visible etermination yer of elling spectral . in gy, EARSEL, niv. of ., Ferrari ,G., nd total nbus-7 CZCS". 1, Woods- ii for sediment nsitivity to Y" • an of Geodesy 983, astal Zone West African e most Africa, Study" rieval of com remote :al zone. Symp. on Louse mtial of the ispended 1C Internal Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 Shape and variability of the absorption spectrum of aquatic humus H.Buiteveld* & F.de Jong Delft University of Technology, Netherlands * Present address: RijkswaterStaat, DBW/RIZA, Lelystad, Netherlands R. Spanhoff Rijkswaterstaat, DGW, The Hague, Netherlands M.Donze Kenia laboratories, Arnhem, Netherlands ABSTRACT: Shape and variability of the absorption spectrum of aquatic humus is investigated. The exponential description of the shape is not accurate enough for remote sensing applications. Considerable improvement in the accuracy of the interpretation of airborne reflection measurements may be expected when actually measured absorption spectra of aquatic humus (part of the optical seatruth) are used as input for the deconvolution algorithm. 1 GENERAL INTRODUCTION In numerous studies it has been demonstrated that airborne passive remote sensing of surface water in the optical window may yield a wealth of synoptical information. This information consists of convoluted data of the effect on the light-field of several physical, chemical and biological compounds of interest. Deconvolution is done using 'algorithms'; the results of these calculations are calibrated by a statistical technique against some seatruth measurements on the compounds of interest. The calibrated values are subsequently used for interpolation and extrapolation to construct distribution maps of these compounds. These maps are as yet of limited use due to the noise and variability in space and time observed in the 'constants' yielded by the calibration procedure. This problem increases in importance going from the open ocean to estuaries; in freshwater bodies it may even be greater. A number of factors may contribute to this undesirable situation: 1. Lack of measurements; instrumental noise. 2. Natural noise in the environment. 3. Natural phenomena that are not recognized in the measurements nor covered by theory. 4. Inadequacy of theory; especially nonlinearity in the relationships between concentrations and optical results cannot be treated in a statistically satisfying way, given the amount of noise in the data. When we develop the instrumental and theoretical apparatus to distinguish such factors we can reach a position from which reliability of remote sensing observations in dependence on the quality of instrumentation, seatruth observations and local conditions, can be judged. As a first step it may be expected that 'optical seatruth', consisting of optical measurements in situ and spectroscopy of water samples, will be much more usefull to develop precision in remote sensing than attempts to directly calculate chemical concentrations from airborne measurements. This translation can be separately done with the spectroscopic data. Purpose of our research is to contribute to a program as sketched above. 1.1 Aquatic humus Humus (or yellow substance or gelbstoff) is a general name covering dissolved organic compounds of large molecular weight. Its definition actually consists in the methods of isolation (primarily pore size of the filterpaper) and measurement; such as total organic compounds, extinction and fluorescence, or any more elaborate set of properties. Pure water has fixed optical properties. Humus has a variable concentration and variable optical properties (Zepp and Schlotzhauer 1981; Bricaud et al. 1981). Together these two determine the optical background in which the contribution from particulate material must be studied. The optical properties of water were reviewed by Smith and Baker (1981). In the present paper the absorption spectrum of humus is discussed. The shape of the absorption spectrum of humus can in first approximation be described by an exponential function (Kalle 1966); absorption decreases strongly with wavelength in a monotonous fashion. a(A) = A e d(A_Ao) (i) with a(A) = measured absorption coefficient in m 1 A = wavelength in nm A 0 = arbitrary constant in nm A,d = calculated by least squares This exponential form is usually applied in marine optics (Prieur and Sathyendranath, 1981). The accuracy of this description was studied by Bricaud et al. (1981) and Zepp and Schlotzhauer (1981). In this model A may be roughly equated with the concentration of humus, while d roughly describes the shape of the spectrum. In fact both parameters depend on the choice of Ao, the measured wavelength range and individual deviation from the model. Zepp and Schlotzhauer (1981) observed that values for A do correlate with total organic carbon, with an uncertainty of a factor of about 2. Bricaud et al. (1981) determined the constant d using a linear regression fit to equation 1 in the range 375-500 nm. The value of d varied from -.02 to -.01 nm 1 , with a mean of -.014 nm 1 . Zepp and Schlotzhauer (1981) found, in the case of freshwater humus, d values between -.0116 and .0175 nm 1 , with a mean value of -.0145 nm 1 , using the wavelength range 300-500 nm. The exponential function (1) with d = -.014 nm 1 is often used as model for the humus absorption. But it appears that the variability of the absorption spectrum of humus in nature and the deviation from the exponential function, with fixed d, are considerable. 2 MATERIALS AND METHODS Samples of surface water were collected at 10 different locations in The Netherlands.

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