Converts LANDSAT image pixels into physical reflectance values.
Transforms images into a standard form so that images acquired by the five Landsat satellites can be compared. The image data from the different satellites are not directly comparable because their scanners are not calibrated the same, and also because the images will have different angles of solar illumination.The digital values of an MSS image are converted to physical reflectance values. The units of the resulting real data output are in 100's of percent albedo.
- IN
- Input image. The input image may contain BYTE, INTEGER*2, INTEGER*4, or REAL*4 data. Window and/or band options may be specified.
- OUT
- Output image. A single-band REAL*4 output image is created. The output image contains the reflectance values of the input image. This image can then be compared to other images that have been transformed by ALBEDO.
- LANDCC
- Landsat Calibration Constant. Valid values for LANDCC are 1 through 7. This constant is a code number representing the satellite and data capture date. Valid values and the description of each are shown below.
CODE SATELLITE CAPTURE DATE ---- --------- ------------ 1 Landsat 1 All dates 2 Landsat 2(a) Prior to 7/16/75 3 Landsat 2(b) After 7/16/75 4 Landsat 3(a) Prior to 6/01/78 5 Landsat 3(b) After 6/01/78 6 Landsat 4 All dates 7 Landsat 5 All dates
- SUNANG
- Sun angle. SUNANG specifies the angle of the sun above the horizon. It is measured in degrees between 0 and 90.
SUNANG is used for adjusting image data values with a sine function to simulate data acquisition with an overhead sun--thus removing solar illumination angles as a source of variability when comparing different images. Note: Sun angle information for each Landsat scene is contained in the CCT header records.
- DARKLEV(0,0,0,0)
- Dark level. The data values which represent dark levels for Landsat 1, 2 and 3 MSS bands 4,5,6,7 and Landsat 4 and 5 MSS bands 1,2,3,4 are entered in band order. Valid values range from 0 to 255. The default values represent the minimum valid digital pixel value.
Dark levels can be used to adjust the lower brightness value for a band from zero to a user specified value. For example, if the minimum pixel value of a band is 15, then the user can set the dark level for that band at 15. In that band, the albedo will be computed after subtracting 15 from each digital pixel value. For any pixel values equal to or below DARKLEV, the albedo for that band will be the computed from the pixel value zero.
The albedo from Landsat 2 data captured after 7/16/75 and with a sun angle of 48.3 degrees will be computed. The entire image and all four bands of INLAND are processed.
The albedo from Landsat 1 data with a sun angle of 80 degrees will be computed. Only two bands are processed. Since the bands of Landsat 1 have an offset of three, bands 3 and 2 represent actual Landsat bands 6 and 5, respectively.
The albedo from Landsat 3 data captured prior to 6/01/78 and with a sun angle of 28.3 degrees will be computed. The two input bands 2 and 1 are offset by three, representing Landsat 3 bands 5 and 4, respectively.
The albedo from Landsat 3 data captured after 6/01/78 with a sun angle of 45 degrees, and dark levels of 8 for band 4, 18 for band 5, 12 for band 6, and 0 for band 7 will be computed.
The albedo from Landsat 5 data with a sun angle of 28.3 degrees will be computed. The input bands of 2 and 1 represent Landsat 5 bands 2 and 1, respectively.
For each data line, all bands are read; their values are translated to real albedo values through the look-up tables and added together to create an output line in real format.
The basic equation used to compute the albedo of a Landsat image is: (See user note 4 for algorithm reference.)
Albedo = 10,000 * 1. / SIN(sunangle) * --- 4 | pixel value (band) SUM | PI / I(band) * { ----------------- * band=1| Range(band) --- --- | [Rmax(band) - Rmin(band)] + Rmin(band)} | | where: --- Rmax = Maximum radiance (mW/cm2/sr), measured by the scanner in each band, Rmin = Minimum radiance (mW/cm2/sr), measured by the scanner in each band, sunangle = Sun angle in degrees from the horizon, I = Solar irradiance (mW/cm2) at the top of the atmosphere in each band, Range = Number of bins in the band. Band 4, 5, and 6: 0 through 127 for Landsat 1, 2, 3, 4, and 5 (all dates). Band 7: 0 through 63 for Landsat 1, 2, and 3 (prior to 06/01/78). 0 through 127 for Landsat 3 (after 06/01/78), 4, and 5. Note: Rmax, Rmin, and I are tabularized by satellite and time since launch. In addition, once sunangle is known, translation tables can be established for possible data values in all four bands, reducing computational requirements to: 4 Albedo = 10,000 * SUM Reflectivity(band), Band=1 where: Reflectivity(band) = PI / [I(band) * SIN(sunangle)] * { [Pixel value (band) / Range(band)] * [Rmax(band) - Rmin(band)] + Rmin(band) }
The maximum number of bands is limited to 4. Since the multispectral scanners in Landsat images measure radiation reflected from the Earth's surface in four bands, these are the only bands used for processing.
Indicates that the user supplied an invalid band number in the input band option. Valid values are 1, 2, 3, and 4.
For Landsat 4 and 5 MSS images, the band option specified directly reflects the MSS bands to be used to compute the albedo.
Examples:
IMAGE.MSS(:1,2,3,4) references MSS bands 1, 2,
3, and 4.
IMAGE.MSS(:2,4) references MSS bands 2 and 4.
IMAGE.MSS(:2,1) references MSS bands 2 and 1.
For Landsat 1, 2, and 3 MSS images, reflected radiation is measured in bands 4, 5, 6, and 7. Therefore, an offset of 3 is used to determine which MSS bands correspond to the band option specification.
Examples:
IMAGE.MSS(:1,2,3,4) references MSS bands 4, 5,
6, and 7.
IMAGE.MSS(:2,4) references MSS bands 5 and 7.
IMAGE.MSS(:2,1) references MSS bands 5 and 4.
Charles J. Robinave, "Computation with Physical Values from Landsat Digital Data," Photogrammetric Engineering and Remote Sensing, Vol. 48, No. 5, 1982, pp. 781-784.