AVHRRAD also looks for the SLOPES and INTERCEPTS lines in the text segment as in visible channel calibration. If these lines are not present in the text segment, then AVHRRAD will try to extract additional information from the text segment in order to compute the slope and intercept values for AVHRR thermal channels 3, 4, and 5. The format of this additional information in the text segment is as follows:
PRT(1): 403.000000 PRT(2): 410.000000 PRT(3): 401.000000 PRT(4): 404.000000 BLACKBODY(3): 613.000000 BLACKBODY(4): 320.000000 BLACKBODY(5): 317.000000 SPACE(3): 993.000000 SPACE(4): 993.000000 SPACE(5): 999.000000 AVALUES(1): 277.018 0.05128 0.0 0.0 0.0 AVALUES(2): 276.750 0.05128 0.0 0.0 0.0 AVALUES(3): 276.862 0.05128 0.0 0.0 0.0 AVALUES(4): 276.546 0.05128 0.0 0.0 0.0These lines can appear in any order in the text segment. The PRT, BLACKBODY, and SPACE lines are required. An error will result if they are not found. The AVALUES lines are optional if the satellite is one of: NOAA-9, NOAA-10, NOAA-12, NOAA-14. The reason for this is that AVHRRAD knows the A values for these satellites. For all other satellites, the A values are not known. They must be acquired and then entered into the text segment as AVALUES lines before performing a thermal channel calibration.
The four PRT lines are the 4 platinum resistance temperature counts. Each is a mean count obtained when a platinum resistance thermometer is used to measure the temperature of the internal blackbody target. These counts can be converted directly to temperature using a formula described in NESS 107 (See the AVALUES description below). Four thermometers are used because of the need for redundancy.
The three BLACKBODY lines are the mean counts obtained when the AVHRR sensor is viewing the internal blackbody target. BLACKBODY(3) is the count associated with AVHRR channel 3, BLACKBODY(4) is associated with AVHRR channel 4, and BLACKBODY(5) is associated with AVHRR channel 5.
The three SPACE lines are the mean counts obtained when the AVHRR sensor is viewing space. SPACE(3) is the count associated with AVHRR channel 3. SPACE(4) is associated with AVHRR channel 4, and SPACE(5) is associated with AVHRR channel 5. The presence of SPACE(1) or SPACE(2) lines in the text segment is ignored by AVHRRAD.
The 4 AVALUES lines are used to convert PRT counts to temperature. For example, the first line (AVALUES(1)) contains 5 coefficients which are used to convert the PRT1 count value into a temperature value in units of degrees Kelvin (K).
PRT, BLACKBODY, and SPACE lines are automatically generated by MIAVHRR or FIMPORT into the text segment (for all AVHRR formats). However, the AVALUES lines must be supplied by the user.