IR spectral imagers are being considered for air to ground target detection applications. IR Fourier transform spectrometers have been used to make field measurements of targets and background. Analysis of these measurements has shown the presence of target to background color and the high spectral band to band correlation of many backgrounds. Detection of low contrast targets in high thermal clutter backgrounds can therefore be improved by using IR spectral sensors as opposed to broad or single narrow band IR sensor. However, the improvement requires a high quality IR spectral sensor. In particular, the sensor must be able to achieve low noise levels. This paper establishes, parametrically, the relationships between ground resolution distance, range, aperture size, spectral bandwidth, integration time, and sensor noise level. Likely required sensor noise levels for target detection are taken from previous estimates based on Fourier transform spectrometer data. Current performance of IR detector arrays is established from the open literature. Using these inputs and making reasonable assumptions as to the values of the other parameters, the trade space between detector array size, ground coverage rate, and sensor noise level is explored.