User's Guide

CLAVR

Cloud mask AVHRR data (NOAA-11 through NOAA-19)

Function:

Creates a cloud mask for AVHRR single-scene or composite data for NOAA-11 through NOAA-17 satellites. The cloud mask is computed using modified NOAA CLAVR-1 and CLAVR-x algorithms. The mask is either written to a user-supplied output file or added as the last band of the input file.

Parameters:

IN
Input image. The input image can either be a single-scene AVHRR image or a composite AVHRR image. A single-scene image must be a 5-band LAS image created by running AVHRRIN and calibrated using AVHRRCAL. A composite image must be a 13-band composite of single-scene images. (See User Notes for expected band order and descriptions).

SATNUM
Satellite number. The 2-digit satellite number assigned by NOAA.

 = 11:  NOAA-11
 = 12:  NOAA-12
 = 14:  NOAA-14
 = 15:  NOAA-15
 = 16:  NOAA-16
 = 17:  NOAA-17

SCALING
Input image scaling type. The scaling type that was applied to the input image by AVHRRCAL.

 = NONE:   No scaling
 = US:     US scaling applied
 = GLOBAL: GLOBAL scaling applied

ACQDATE
Input image acquisition date. This parameter is a 3 value integer array. The date is entered as month, day and 4-digit year. For single-scene input images this is the acquisition date of the image. For composite input images this is the median acquisition date of individual scenes that went into the composite.

THRESHOLD(--)
Threshold file name. File containing alternate threshold values for the various CLAVR tests. (See User Note 1 for example file).

BARREN(--)
Barren mask image. A binary image where pixels deemed to be void of vegetation (barren) have the value 1 and all others 0. The image must be the same size and projection as the composite input image. If input image is a single-scene, this parameter is ignored (See User Notes).

OUT(--)
Output image. If supplied, the output image will contain the cloud codes for the input image. If left NULL, the cloud codes will be added as the last band to the input image.

Examples:

  1. LAS> clavr in=ah16051402114532 satnum=16 scaling=none acqdate=(5 14 2002) out=cld_ah16051402114532

    The single-scene input image AH16051402114532 was acquired on May 14, 2002 and calibrated without any scaling. The cloud mask will be written to a separate image CLD_AH16051402114532.

  2. LAS> clavr in=us01_060073 satnum=14 scaling=us acqdate=(3 8 2001) barren=us_barren

    The US composite US01_060073 was created with "US" scaling and the median acquisition date of the individual scenes was Mar 8, 2001. The barren mask image, US_BARREN, will be used in the masking algorithm. The cloud mask will be added as the 14th band to the input image.

  3. LAS> clavr in=us_02287301 satnum=16 scaling=us acqdate=(9 21 2002) threshold=sep_test_thresholds out=sep_test_mask

    The US composite US_02287301 was created with "US" scaling and the median acquisition date of the individual scenes was Sep 21, 2002. A threshold file, SEP_TEST_THRESHOLDS, will be used to override default threshold values for September. The cloud mask will be written to SEP_TEST_MASK.

Description/Algorithm:

The input parameters are obtained and checked for validity. The type of input, single-scene or composite, is determined. If a valid addr and mnr file exist the input scene is considered a single-scene. If the addr and mnr file exist, but are not valid, a fatal error occurs. If the addr and mnr file do not exist then the input is considered a composite. All input files are opened and checked for validity. The cloud codes are determined by subjecting each pixel in the input image to a series of tests. The tests were derived from the NOAA CLAVR-1 and CLAVR-x algorithms. The output cloud codes are either written to a user supplied image or added as the 6th or 14th band of the input image.

User Notes:

  1. The threshold file contains alternate threshold values for one or more of the CLAVR algorithm tests. The file must be a text file. Each line of the file must consist of a test name, white space and threshold value. Only valid test names are permitted in the file. If an invalid test name, or a test name without a value is encountered, a fatal error occurs. The test name/value pairs may be listed in any order and are not case sensitive. If more than one occurence of a test name is present the last one in the file takes precedence and a warning message about duplicate test names will be issued. Default values from ADAPSTABLES are loaded prior to user-supplied values which take precedence over default values. See the Stowe, et al reference listed in the Requirements Specification document for an explanation of the tests. Example file containing all valid test names:

        RGCT 44.0
        TGCR1 293.0
        C3AR 3.0
        C3AR_KLM 5.0
        C3AR_KLM3A 5.0
        Gamma 50.0
        RRCT_min 0.9
        RRCT_max 1.1
        TGCR2 293.0
        C3AT 6.0
        C3AT_KLM 6.0
        C3AT_KLM3A 15.0
        TGCT 249.0
        LAT_max 60.0
        LAT_min -60.0
    

  2. Single-scene AVHRR image. This is a LAS image created by AVHRRIN with associated files addr and mnr. The input must contain calibrated, percent reflectance, AVHRR channel 1 through 5 data. It must contain only 5 bands and be in channel 1-5 sequence.

  3. Composite AVHRR image. This is a LAS image containing one or more single AVHRR scenes. The image ddr must contain valid projection information. Bands 1-5 must contain AVHRR, calibrated, percent reflectance channels 1data, in that order. Bands 7, 8 and 9 must be satellite zenith, solar zenith and relative azimuth angles. Band 12 must contain a QC band. The QC band will only be used to determine the presense of channel 3A or 3B in KLM series satellites. It must contain a total of 13 bands.

  4. This implementation of CLAVR cannot cross-reference latitude and longitude information between the AVHRR model (satellite projection) and other projections. Therefore, if a barren mask is supplied with a single-scene input image, the barren mask will be ignored.