DAIS Data Processing
	German Aerospace Center

Due to the optomechanical and electronical characteristics of the instrument, all data must undergo a special preprocessing and calibration procedure before any quantitative analysis (Strobl et al., 1996). For this purpose a software package was designed, which is intended to fulfill the requirements of an operational and mostly automatical preprocessing of the airborne imaging spectrometer data. Four main software design requirements had to be met. Fast processing using as little disk space as possible Modular design, allowing user guided stepwise execution as well as noninteractive processing Steady recording of all relevant parameters and comprehensive reporting Exact repeatability of all processing steps at any time in the future Fig. 1: Schematic overview of DAIS preprocessing steps Data preprocessing to level 1 takes place in three steps which are realized by two software modules. During the first step the raw data are read from tape, converted to BSQ format and written to hard disk. At the same time auxiliary data are extracted. A raw data report is issued which contains quicklooks and histograms of all channels as well as a summary of auxiliary parameters. The converted raw data are then automatically archived to an ADSM tape roboter at the computing center. Thus the data must only be read from tape once. JPEG quiklook images and a browsable list in HTML format are automatically generated and maintained. This list is not yet available to the public, an example of what it looks like is given in the DAIS project page. The HTML catalogue serves as well as an index to locate specific raw files in the archive for retrieval and system correction. The system corection procedure first detects and removes bad lines before performing the dark current subtraction and the correction of the AC-coupled channels. Thereafter the calibration coefficents may be applied as the third and last step of the radiometric preprocessing. At the end of the Level 1 processing 3 files will be issued for each data take: Filetype Extension 1. The imaging spectrometer data as a binary integer file in BSQ format .bsq 2. An ASCII header file in the ENVI format .hdr 3. The Auxiliary Database in XDR (eXternal Data Representation) format .aux The operator receives a printed report comprising the processing steps and allowing data quality asessment through parameters such as histogram and SNR for each channel and channel cross correlation analysis. To visualize the effect of image enhancements, report pages may be printed for selected channels. The atmospheric correction is based on the MODTRAN radiative transfer code (Berk et al., 1989). Image data in the reflective channels of the DAIS sensor are converted to ground reflectance. From the thermal channels emissivities and surface temperatures are derived. Special features include the calculation of water leaving radiance, radiation fluxes and heat fluxes (Richter, 1996). To assess the stability of the sensor calibration an interactive user-friendly software was developed to carry out an inflight calibration based on measurements of selected ground targets and observed atmospheric data. A fully parametric georectification program called PARGE is being developed by Daniel Schläpfer at the Remote Sensing Laboratories (RSL) of the University of Zurich. Given a digital elevation model and differential GPS aircraft position measurements this softare performs a geocoding of DAIS 7915 data. Differential GPS data have been recorded for most of the flights since 1997 and are made available upon request (please contact: Andrea Hausold).

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