Prelaunch algorithm and data format for the Level 1 calibration products for the EOS-AM1 Moderate Resolution Imaging Spectroradiometer (MODIS)

-The MODIS radiometric calibration product (Level 1B) is described for the thermal emissive and the reflective solar bands. Specific sensor design characteristics are identified to assist in understanding how the calibration algorithm software product is designed. The reflected solar band software products of radiance and reflectance factor both are described. The product file format is summarized and the MCST Homepage location for the current file format is provided. Guenther and Montgomery are employed by NASA's Goddard Space Flight Center, Greenbelt, MD 20771. Godden is employed by Physics Application, Inc, Vienna, VA 22182 Xiong is employed by Science Systems and Applications, Inc, Lanham, MD 20706 Knight and Khayat are employed by Research and Data Systems Corporation, Greenbelt, MD 20770 Qiu is employed by Computation Physics Applications, Inc. Columbia MD 21042 Hopkins and Hao are employed by General Sciences Corporation, Laurel, MD 20707 Corresponding Author: B. Guenther, Mail Code 920.1, GSFC, Greenbelt, MD 20771; telephone (301)2865205; fax (301)286-0373; email: [email protected] 1.0 Introduction This paper describes the MODIS calibration data product. The calibration equations for this product are developed and the approaches for the laboratory calibration and the on-orbit verification of that calibration are described also. The development of the MODIS science products begins with the Level 1B calibration products. The radiometric characteristics of the LIB product are reviewed, but the geometric registration and spectral characterization of the products are not described in this paper. The primary aspects of the MODIS sensor is discussed by Barnes [1]. Major science products for the MODIS oceans [2] and land surface [3] research communities are described elsewhere in this issue. Sensor design and characteristics necessary to understand the Level 1B software product are reviewed in the Section 2.0, Instrument Background. The emissive infrared algorithms are described in Section 3.0. The reflected solar bands algorithm, including subsections on the radiance and the reflectance factor products, is covered in Section 4.0. The Level 1B data software product attributes such as file format and uncertainty index are reviewed in Section 5.0. The conclusion and summary comments are provided in Section 6.0. 2.0 Instrument Background The MODIS is a 36-band spectroradiometer which covers a broad spectral range, and has very demanding calibration performance characteristics. The sensor design incorporates a paddle-wheel scan mirror to provide a wide swath across the Earth surface, and to provide access to an array of characterization sub-systems on each rotation of the mirror. The spectral separation of the light comes from three dichroics and sliver interference filters at each detector. The spectral ranges for the reflected solar bands (0.4 to 2.3 _m) and the emissive infrared bands (3.6 to 14.4 prn) calibrated and analyzed with separate techniques. The descriptions of the calibration approach and algorithm follows this separation. Figure 1 provides a schematic of the sensor optics, optical detectors and electronics to demonstrate how optical signals onto the scan mirror are transformed to digital signals or data. The MODIS design incorporates several on-board calibration (OBC) targets and each is valuable for some aspect of the calibration algorithm design. The scan mirror points to the internal OBCs: the solar diffuser (SD), the spectroradiometric calibration assembly (SRCA), the blackbody (BB) and cold space view (SV) on each mirror rotation. The scan mirror is double sided and both sides are used for the MODIS observations. A rotation of 360 degrees of the scan mirror requires 2.954 sec. Throughout this paper, a period of 1.477 sec is identified as a scan, and the data produced from it is called a scan line of data,