noise_pert.c

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/*
  This file is part of the AIRS Code Collection.
  
  the AIRS Code Collections is free software: you can redistribute it
  and/or modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation, either version 3 of
  the License, or (at your option) any later version.
  
  The AIRS Code Collection is distributed in the hope that it will be
  useful, but WITHOUT ANY WARRANTY; without even the implied warranty
  of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with the AIRS Code Collection. If not, see
  <http://www.gnu.org/licenses/>.
  
  Copyright (C) 2019-2025 Forschungszentrum Juelich GmbH
*/
 
#include "libairs.h"
 
int main(
  int argc,
  char *argv[]) {
 
  static pert_t *pert;
  static wave_t wave;
 
  FILE *out;
 
  char pertname[LEN];
 
  double mu, nedt = -1e99;
 
  /* Check arguments... */
  if (argc < 4)
    ERRMSG("Give parameters: <ctl> <pert.nc> <noise.tab>");
 
  /* Read control parameters... */
  scan_ctl(argc, argv, "PERTNAME", -1, "4mu", pertname);
  int bsize = (int) scan_ctl(argc, argv, "BSIZE", -1, "-999", NULL);
  const double maxvar = scan_ctl(argc, argv, "MAXVAR", -1, "-999", NULL);
 
  /* Allocate... */
  ALLOC(pert, pert_t, 1);
 
  /* Read perturbation data... */
  read_pert(argv[2], pertname, pert);
 
  /* Set block size... */
  if (bsize < 0)
    bsize = pert->nxtrack;
 
  /* Create file... */
  printf("Write noise data: %s\n", argv[3]);
  if (!(out = fopen(argv[3], "w")))
    ERRMSG("Cannot create file!");
 
  /* Write header... */
  fprintf(out,
          "# $1 = longitude [deg]\n"
          "# $2 = latitude [deg]\n"
          "# $3 = mean brightness temperature [K]\n"
          "# $4 = noise estimate [K]\n\n");
 
  /* Loop over granules... */
  for (int itrack = 0; itrack < pert->ntrack; itrack += bsize) {
 
    /* Convert retrieval data to wave struct... */
    pert2wave(pert, &wave, itrack, itrack + bsize,
              pert->nxtrack / 2 - bsize / 2, pert->nxtrack / 2 + bsize / 2);
 
    /* Estimate noise... */
    double nedt_old = nedt;
    noise(&wave, &mu, &nedt);
 
    /* Write output... */
    if (maxvar <= 0
        || fabs(200 * (nedt - nedt_old) / (nedt + nedt_old)) < maxvar)
      fprintf(out, "%g %g %g %g\n", wave.lon[wave.nx / 2][wave.ny / 2],
              wave.lat[wave.nx / 2][wave.ny / 2], mu, nedt);
  }
 
  /* Close file... */
  fclose(out);
 
  /* Free... */
  free(pert);
 
  return EXIT_SUCCESS;
}