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Airborne hyperspectral remote sensing enables not only spatial monitoring of vegetation\ncover, but also the derivation of individual plant constituents such as chlorophyll and\nnitrogen content. These are important parameters for optimised agricultural management\non a field basis through the possibility of spatially differentiated fertilisation and for\nhydrological and vegetation yield modelling.\nThe use of existing airborne imaging spectrometers is cost-intensive. Moreover, it is\ndifficult to obtain these sensors for multitemporal applications. The imaging spectrometer\nAVIS (Airborne Visible/Near Infrared Imaging Spectrometer) was built at the Chair of\nGeography and Geographical Remote Sensing of the Ludwig Maximilians University\nMunich, Germany, to overcome these difficulties. AVIS is designed as a cost-effective tool\nfor environmental monitoring using commonly available components. AVIS enables the\ndeployment of a hyperspectral sensor for both scientific research and educational\npurposes. It is based on a direct sight spectrograph coupled to a standard B/W CCD\ncamera. The signal received by the CCD is read out and sent via a frame grabber card to a\npersonal computer, where the data is stored on the hard disc together with additional GPS\ndata. The radiometric, spectral and geometric properties of AVIS resulting from the\ncalibration procedure are summarised in Table 7-1.\nTable 7-1: AVIS characteristics\nParameter Description\nSpectral range 553-999nm\nSpectral resolution 6nm\nSpectral sampling rate / resampling 2nm / 6nm\nNumber of used bands 74\nSNR 45dB (year 1999), 47dB (year 2000)\nSpatial resolution 300 pixels per image line\nSpatial sampling rate 390 pixels per image line\nFOV 1.19rad\nIFOV across track 3.1mrad\nIFOV along track 2.98mrad\nOne aim of this thesis was to test the potential of AVIS for the purpose of environmental\nmonitoring, especially of the chlorophyll and nitrogen status of plants. The land cover\ntypes under investigation were grassland, maize ( Zea mays L.) and winter wheat ( Triticum\naestivum L.). Within this scope, a total of 21 AVIS flights were carried out during the\nvegetation periods of the years 1999 and 2000. The AVIS data were preprocessed before analysis, including dark current and flat field correction, resampling as well as atmospheric\ncorrection and reflectance calibration.\nThe test area chosen for the validation of the AVIS data is located in the northern\nBavarian foothills, 25km southwest of Munich, Germany (48\xb0 6\u2019 N, 11\xb0 17\u2019 E). It is situated\nbetween the Ammersee in the west and the Starnberger See in the east. The\nmunicipalities Gilching and Andechs define the northern and southern borders\nrespectively.\nWithin this area, three water protection areas were chosen as test sites. In these test\nsites, most of the farmers are under contract to the local agricultural office \u201c Amt f\xfcr\nLandwirtschaft\u201d resulting in detailed management data for each field. This data include\nuseful information for the interpretation of ground and AVIS data. Two weather stations of\nthe Bavarian network of agro-meteorological stations, namely No.72 (Gut H\xfcll) and No.80\n(Rothenfeld), are located in the test area and provide information about precipitation,\ntemperature and radiation. Ten and thirteen stands were selected as test fields in 1999\nand 2000 respectively, including three fields each of maize and wheat in 1999 as well as\nthree fields of maize and six fields of wheat in 2000. During both years, four meadows\nwere investigated belonging to the same plant community ( Arrhenatherion elatioris). The\nmeadows differ in the utilisation intensity (non-fertilised meadow with one cut, meadow\nwith one cut, meadow with rotational grazing and meadow with four to five cuts).\nThe ground truth campaigns included weekly measurements of plant parameters, such as\nheight, dry and wet biomass, phenological stage, chlorophyll and nitrogen content, as well\nas a photographic documentation for each field.\nThe chlorophyll and nitrogen measurements, which were derived from the sampling on\nground, are available in contents per area [g/m\xb2] and in contents per mass ([mg/g] for\nchlorophyll and [%DM] for nitrogen). The former can be used to evaluate the\nphotosynthetic capacity or productivity of a canopy, which is an important input parameter\nfor hydrological or vegetation models; the latter may be an indicator for plant physiological\nstatus or level of stress, which is a valuable source of information for optimising field\nmanagement.\nThe relationship between chlorophyll and nitrogen based on the ground measurements\nshowed that a differentiation of the land cover types is necessary for significant\ncorrelation. When the plant species are investigated separately, the chlorophyll and\nnitrogen content per area are always highly correlated, especially for chlorophyll a and\ntotal chlorophyll content (r\xb2\u22650.8). For all investigated land cover types, the nitrogen and\nchlorophyll contents per mass are uncorrelated. For wheat, the results improve when the\nphenological state and the cultivar are considered (r\xb2>0.67). For maize, distinct variations\nin the chlorophyll content per mass during the vegetation period reduced correlation with these parameters. The use of a fitted chlorophyll trend curve instead of the original\nmeasurements does not lead to a significant improvement of the results.\nFor grassland, no significant correlation above r\xb2=0.67 could be observed except for\nchlorophyll and nitrogen, both per area, where a decreasing strength of correlation could\nbe monitored with increasing fertilisation level.\nThese results lead to the conclusion that the chlorophyll and nitrogen contents per mass\nof the investigated land covers are decoupled when the compensation point for effective\nphotosynthesis is exceeded. Beyond this limit the nitrogen in the plants is no longer\nincorporated into chlorophylls, but mainly into proteins, alkaloids and nucleic acids,\nwhereas the proteins especially are used for internal storage of nitrogen.\nThe derivation of the chlorophyll and nitrogen content of the plant leaves on a mean field\nbasis was conducted using three hyperspectral spectral approaches, namely the\nhyperspectral NDVI (hNDVI), the Optimised Soil Adjusted Vegetation Index OSAVI as well\nas the relatively unknown Chlorophyll Absorption Integral CAI. The multispectral NDVITM\nwas simulated as established reference.\nThe results of the derivation of both chlorophyll and nitrogen content of plants with the\ninvestigated approaches depend strongly on a priori knowledge about the canopies\nmonitored. In general, the use of contents per area rather than contents per mass has\nbeen found more suitable for the investigated remote sensing applications.\nA significant correlation between any index and the chlorophyll or nitrogen content for the\nwhole sample size could not be derived. The optimal spectral approach for derivation is\nspecies-dependent, but also dependent on the cultivar. The chlorophyll and nitrogen level\nof the plants under observation as well as their temperature sensitivity mainly caused this\ndependence. The NDVITM, hNDVI and OSAVI became insensitive for high chlorophyll\ncontent above about 1g/m\xb2 (1.5mg/g) chlorophyll a and 0.2g/m\xb2 (0.4mg/g) chlorophyll b,\nrespectively. A saturation of the indices was also found for nitrogen content above\n2.5g/m\xb2. The saturation limit of nitrogen in percentage of dry matter could be rated at\nabout 4%. The positive correlation between the indices and this parameter for wheat\nleads to insensitivity at values above this limit, while the negative correlation for maize\nresults in saturation for values below 2.5%.\nThe CAI is not affected by saturation as much as the other spectral approaches, leading to\nhigher coefficients of determination, especially for contents per area. The CAI becomes\ninsensitive at chlorophyll contents per area above 2g/m\xb2. The results lead to the\nassumption, that the flattening and narrowing of the chlorophyll absorption feature at\n680nm most probably causes the saturation of the NDVITM, hNDVI and OSAVI. The ratios\nare directly affected by an increase in reflectance in the red wavelength region. The high\ncorrelations between the CAI and contents per area can be ascribed to the fact that the\nCAI is based on an integrated measurement over an area and therefore is less affected by an increase of reflectance in the red wavelengths. The CAI probably becomes insensitive\nat the point where the narrowing of the absorption feature leads to a shift of the red edge\nposition towards the blue wavelength region. This saturation limit lies at approximately 2g\nchlorophyll per m\xb2.\nIn contrast, the chlorophyll content per mass, which indicates the plant\u2019s physiological\nstatus or level of stress, could be estimated more accurately using spectral indices such as\nhNDVI and OSAVI, especially for wheat. The low correlations derived for maize are caused\nby its higher temperature dependence, leading to daily variations in the chlorophyll\ncontent per mass.\nThe chlorophyll and nitrogen contents of the grassland canopies could not be derived with\nthe spectral approaches investigated. When the meadows were investigated separately,\ncorrelations could only be found between the CAI and the chlorophyll content per area for\nthe most intensely utilised meadow (four to five cuts), which on the one side is\ncharacterised by the highest level of fertilisation, but on the other side is affected by the\nhighest nutrient offtake. The low potential of the investigated indices can be mainly\nassigned to the fact that the chlorophyll and nitrogen values of the meadows mostly\nexceeded the saturation limits of the applied indices.\nThe possibility of deriving chlorophyll and nitrogen accurately enough to map within field\nheterogeneities was discussed on the basis of a wheat field, which was analysed\nseparately at three sampling points for chlorophyll and nitrogen content. The approaches\nfound to be most suitable for the parameter estimation of wheat were applied. The CAI\nwas used for the estimation of the chlorophyll content per area and mass as well as for\nthe nitrogen content per area. The hNDVI was applied to estimate the canopy\u2019s nitrogen\ncontent per mass. Both approaches were able to reproduce the chlorophyll contents of the\ndifferent sampling points accurately enough to derive the differences between the\nmeasurement points when the saturation limits were not exceeded. Beyond these limits\nthe index values decreased with increasing measurement values.\nThe spatial pattern of the nutrient supply was discussed by comparing nitrogen pattern\nimages, which were derived from CAI measurements acquired in 2000 with the yield\nmeasurement map of the same field. The phenological stage of stem elongation (EC 30)\nturned out to be most suitable for the derivation of the nitrogen pattern. On the one hand,\nthe crop condition at these stages determine yield and on the other hand the nitrogen\npattern images were able to map the inner field patterns of nitrogen supply. After anthesis\nthe nitrogen images can map areas with different degrees of maturity. Therefore they can\nbe used for the monitoring of maturity stages for the determination of the most favourable\nharvest date.\nAs described here, AVIS is still in its early stages. It has the potential to become a costeffectiveAVIS2, which covers the spectral range of 400-900nm, has been in commercial use since\n2001.\ntool for the monitoring of the environment. A modification of AVIS, namely