Modeling of the radiometric characteristics of a simulated fluorescent imager

The purpose of this study was to determine whether changes in stimulated plant fluorescence could be detected by a remote sensing system. By measuring the changes in fluorescent signal the health status of vegetation can be determined. The plant condition can be assessed by viewing the ratio 690 nm/ 730 nm from the fluorescent spectra at the leaf level. The question is whether the change in fluorescent spectra (change in the ratio) can be seen at a remote location. In order to address this question a theoretical scenario was developed and the expected signal at a remote location was determined through radiometric calculations. The scenario involved determining the signal, at three different standoff distances, from a soybean plant under six different plant conditions. The fluorescent signal of a plant at the leaf level was taken (from previous research) and the effects of the canopy factored into the signal. This was accomplished through use of a theoretical canopy model. Lowtran was used to model the atmospheric effects. The atmospheric and sensor system effects were incorporated through a series of radiometric calculations. This provided the fluorescent ratio (690 nm/730 nm) for three different sensor standoff distances and six different plant conditions. It was found that the six different soybean conditions could be distinguished from one another when measured at a standoff of 10 or 30 meters. In order for all six conditions to be distinguished, the canopy density of the plant had to have a value above 1 and 1.5 in the 10m and 30 m cases. Also the measured signal had to be averaged over four detector resolution elements. In the case of a 300 meter standoff the different plant conditions could be seen if the plant canopy had a leaf area index (canopy density) of at least 2.3 and the signal was averaged over 16 resolution elements. The collection conditions, leaf area index, canopy structure, soil reflectivity, atmospheric conditions, and sensor system response were all found to affect the fluorescent ratio measured