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Design and Testing of a Global Positioning System-Based Radiometer for Precision Mapping of Pearl Millet Total Dry Matter in the Sahel

^a Inst. of Animal Production in the Tropics and Subtropics (480), Niamey, Niger
^b International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Sahelian Center, B.P. 12404, Niamey, Niger
^c Unité décologie des grandes cultures, Université Catholique de Louvain, Place Croix du Sud, 2 Bte 11, 1348 Louvain-la-Neuve, Belgium
^d Inst. of Plant Nutrition (330), Univ. of Hohenheim, D-70593 Stuttgart, Germany, presently Inst. of Crop Science, Univ. of Kassel, D-37213 Witzenhausen, Germany

View larger version (37K): [in a new window]   Fig. 1 Diagram of the radiometer operating in a pearl millet field showing its major components

View larger version (18K): [in a new window]   Fig. 2 Block diagram of circuitry common to both versions of the radiometer

View larger version (52K): [in a new window]   Fig. 3 Block diagram of the digital processing circuitry for the `discrete measurement' (instrument 1) radiometer (A) and block diagram of the digital processing circuitry for the `continuous measurement' (instrument 2) radiometer (B)

View larger version (106K): [in a new window]   Fig. 4 Georeferenced red band of the aerial photograph taken on 15 May 1998 of the subarea of trial 1 used for the radiometer calibration. The plot layout and positions of radiometer measurements overlays are shown

View larger version (15K): [in a new window]   Fig. 5 Relationship between plot fractional vegetation cover determined from aerial photography and normalized difference vegetation index (NDVI) values from radiometer measurements

View larger version (15K): [in a new window]   Fig. 6 Relationship between above ground total dry matter (TDM) of individual millet hills and normalized difference vegetation index (NDVI) taken on 24 June 1998 in trial 1

View larger version (19K): [in a new window]   Fig. 7 Comparison of regression polynomials measured for 5 consecutive days during experiment 1b after correction of the normalized difference vegetation index (NDVI) values for the background NDVI of bare soil

View larger version (26K): [in a new window]   Fig. 8 Transect of regularly spaced (0.1, 0.2, and 0.4 m) normalized difference vegetation index (NDVI) measurements over 10 millet hills compared to NDVI measurements centered over plants on 30 June 1998, experiment 1c

View larger version (68K): [in a new window]   Fig. 9 Variability maps for destructive measurements of total dry matter at harvest compared to normalized difference vegetation index (NDVI) values taken 36 d before harvest on a millet field (trial 2) at Sadoré, Niger. Note that the darker areas in the NDVI image represent areas of low plant density. The four low vegetation E-W strips visible on map C correspond to the tracks of the linearily moved wheels of the irrigation system