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Engineering analyses conducted to assess image data quality are described and results are presented for the Landsat-4 Multispectral Scanner (MSS) and Thematic Mapper (TM). Also, coincident data from the two sensors are compared. Macroscopic studies addressed trends and characteristics of full frames of data, while Â¿microscopicÂ¿ studies assessed differences between individual detector responses. Raw data, radiometrically corrected data, and fully corrected data were analyzed, as well as special calibration data. The Landsat-4 MSS was found to produce data of high quality, comparable to previous Landsats, except for a low-level coherent noise effect which is unique to the current sensor. Radiometric relationships between Landsat-2 and -3 MSS's and the Landsat-4 MSS were established through empirical analysis of simultaneously acquired data. The TM was found to produce image data of very good spatial resolution and overall good radiometric data quality, showing improvements over MSS. Radiometric equalization of detector responses was found to be close to the theoretical limit of quantization error, except for two relatively low-amplitude artifacts. One is a difference in response that depends on the direction of mirror scan. This produces scan-angle effects superimposed on scene-related effects. The second is a tendency for level shifts to occur between mirror scans at random times but with correlations between detector responses. Two forms or patterns of level shift were identified, corresponding to four system noise states. Preliminary correction models and/or procedures have been developed and recommended for further evaluation.