Image Quality Data Research Articles

Calibration of thematic mapper thermal data for water surface temperature mapping: Case study on the Great Lakes

The potential utility of Landsat-5 Thematic Mapper (TM) thermal IR (Band 6) data for measuring and mapping surface water temperatures of the Great Lakes is analyzed. Two contiguous TM scenes were collected on 18 July 1984 over the Green Bay-North Central Lake Michigan and Milwaukee-South Central Lake Michigan regions, respectively. The TM thermal IR data were empirically calibrated using surface reference data. The regression model so developed, was then used to map surface temperature (°C) over the entire TM coverage area. Surface reference data points not used in the original calibration were used to test the predictive capability of the model over a wider geographic area. As part of the Landsat Image Data Quality Analysis effort (LIDQA), Bartolucci et al. (1985) have investigated the absolute calibration of TM thermal IR data. Application of these calibration equations to our data set verified their accuracy, resulting in a root mean square error of less than I(/dg)C.

Landsat image data quality studies

The July 1982 launch of Landsat-4 was immediately followed by a two-year comprehensive set of detailed investigations sponsored by the National Aeronautics and Space Administration (NASA) at Goddard Space Flight Center (GSFC). The Landsat Image Data Quality Analysis (LIDQA) research plans for these investigations were specified prior to launch, so that minimum time would be lost in assessing the performance of the long-awaited Thematic Mapper (TM) sensor that Landsat-4 carried in addition to a fourth Multispectral Scanner (MSS). The LIDQA investigations have been substantially completed, and have shown that the TM is a very good spaceborne multispectral radiometer, and has met or exceeded most of its design goals. TM's new short-wave infrared (SWIR) spectral capability yielded improved mineral and plant discrimination compared to the MSS, as anticipated by ground-based and airborne TM simulations. Moreover, the improved spatial resolution and geometric accuracy of Landsat-4 and the TM have resulted in satellite image maps exceeding 1:100,000 U.S. map accuracy standards. Finally, based on an information entropy measure, principal component analysis, and classification results, TM data has been shown to approach its theoretical limit in information content per pixel, exceeding the MSS by at least a factor of two.

Cartographic Accuracy of LANDSAT-4 MSS And TM Image Data

Investigations of the cartographic quality of Landsat-4 MSS and TM image data in CCT-p formats have produced rectification accuracies (rmsexy values) of ± 2/3 to ± 1 data pixel for both whole and subscene areas using polynomials of the first through third degree. In order to achieve these accuracies with MSS data, 15 or more Ground Control Points (GCP's) are required, whereas with the TM data sets as few as 5-10 GCPs will suffice. Factors which limit the cartographic rectification accuracies of the Landsat-4 data include: 1) spatial resolution of the data; 2) map and digitizing errors; and 3) terrain relief. Of these factors, data resolution is the most significant, limiting the location of GCP's to about ± 0.5 pixel. Horizontal displacements due to terrain relief can be minimized by selecting GCP's at or near midrange elevations. Overall, the representative rmsexy values of ±25 and ±55 m for TM and MSS data sets are within U.S. National Map Accuracy Standards for cartographic products of 1:100 000 and 1:200 000 scale, respectively.

Characterization of LANDSAT-4 MSS And TM Digital Image Data

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 "microscopic" 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.

Performance of Positron Imaging Systems as a Function of Energy Threshold and Shielding Depth

The effect of energy discrimination and shielding on positron imaging data quality was investigated using a detector pair to simulate a ring positron emission tomograph. Formulas are presented relating the sensitivity, random fraction, and scatter fraction for a detector pair to the same parameters for a ring system. Data were fitted to detector pair expressions for the variation of the above parameters with shielding depth in order to obtain information on the effect of energy threshold level. These fitted curves were used to determine the sensitivity, random fraction, and scatter fraction, as well as an overall data quality factor as a function of energy threshold level and shielding depth. Data were obtained for both NaI(T1) and BGO detector types using activity levels in the range of 1.5 muCi/cm3. Results show that for NaI(T1) detectors, the lowest possible energy threshold level is optimal, with the corresponding optimal shielding depth determined by the level of activity to be imaged. For BGO detectors, a tradeoff exists between energy thresholds of 100-400 keV and shielding depths of 15-30 cm with smaller shielding depths requiring higher energy thresholds.

A Review of: “Advances in the Quality of Image Data.” Proceedings of the International Society of Photogrammetry and Remote Sensing, Commission I Symposium. Edited by J. C. TRINDER and L. C. HOLSTEIN. (International Archives of Photogrammetry 24 (1), 1982). [Pp. 271.] Price $20.00 Australian.

(1983). A Review of: “Advances in the Quality of Image Data.” Proceedings of the International Society of Photogrammetry and Remote Sensing, Commission I Symposium. Edited by J. C. TRINDER and L. C. HOLSTEIN. (International Archives of Photogrammetry 24 (1), 1982). [Pp. 271.] Price $20.00 Australian. International Journal of Remote Sensing: Vol. 4, No. 2, pp. 482-482.