When it becomes desirable to employ multispectral remote sensing to map a particular environmental insult that is known or suspected to have occurred, it is useful to determine what spectral features are characteristic of the element or chemical compound comprising the environmental insult. This can be done in two general ways: by creating a quantitative algorithm via statistical methods that translates spectral band inputs of a particular remote sensing sensor into content of the element sought or by creating an enhancement image that displays the chemical compound of interest as red (or other color of choice), and almost everything else as other colors. The latter is not quantitative, but can often be helpful even when the quantitative algorithm approach fails. For both of these methods, spectral ratios (that have been dark-objectsubtracted for atmospheric haze correction and sensor electronic offset in the case of the remote sensor data) are employed. Spectral ratios are more robust than single band information, not only for muting brightness variations caused by slope variations in the imaged scene, but also because they are most comparable to spectral ratios of laboratory reflectance spectra that have been averaged over the spectral bands of the remote sensor employed for the mapping. An example will be made for the environmental insult of phosphorous, which is important for both reducing the amount of fertilizers applied to agricultural fields and for controlling cyanobacteria algal blooms (which are sometimes toxic to animals and humans) in nearby lakes and streams.
