<title>Requirements for calibration of focal plane arrays for imaging spectrometers</title>

Abstract

ABSTRACTRecently a new class of instrumentsT that uses a detector array to measure spectra for multiple pointson the ground has become available. These instruments build up an image by a pushbroom technique. Therealization ofthe maximum potential ofthese Array Imaging Spectrometers is dependent on the ability tocorrect pixel to pixel variations in gain, bias, dark current and linearity ofthe detector array. Residualcalibration striping in each band along the temporal axis, is usually the limiting noise source in these sensors,not photon or system electronic noise Indeed, performance calculations or measurements which do not takethis important noise source into account seriously overestimate the performance ofArray ImagingSpectrometers. In this paper, the calibration requirements for Array Imaging Spectrometers, in general, and theprocedure used to calibrate the Airborne Hyperspectral Imager (AHI) will be discussed. Examples from theAirborne Hyperspectral Imager (AHI) will be used to illustrate the residual error and characterize its effect.Key Words: calibration, hyperspectral, AHI1. INTRODUCTIONA new class of sensors, called Array Imaging Spectrometers, differs in several important ways frompredecessor instruments. The direct predecessor to the Array Imaging Spectrometer is the Imaging ArraySequential Filter sensor and the Whiskbroom Imaging Spectrometer. An imaging array instrument(essentially a camera) forms an image by projecting the scene onto the two dimensional detector array, withmultiple spectral bands taken in time sequence usually using a filter wheel. A whiskbroom imagingspectrometer consists of a linear array of detectors, one for each spectral band. The spectrum for a single pointon the ground is projected onto this array, and the image ofthe scene is built up by raster scanning in twodimensions to cover the scene. The Array Imaging Spectrometer projects the spectra ofa line ofpoints on theground (typically 128 to 256)