calculate_footprint_size_amsu

 calculate_footprint_size_amsu Calculate approximate footprint edge

 Calculates the semi-major axis, the semi-minor axis and the eccentricity of
 an ellipse approximating the edge of the AMSU footprint, according to the
 method found in bennartz00:_optim_convol_amsu_b_amsu_jaot, depending on the
 scan position.

 FORMAT

   [cross, along, eccentricity] = calculate_footprint_size_amsu(type, n)

 IN

   type    string  'amsua' or 'amsub'
   n       scalar  channel number

 OUT

   cross   scalar  cross-track size (km)
   along   scalar  along-track size (km)
   ecc     scalar  eccentricity for ellipse

 $Id: calculate_footprint_size_amsu.m 6679 2010-12-10 19:56:54Z gerrit $

0001 function [cross, along, eccentricity] = calculate_footprint_size_amsu(type, n)
0002 
0003 % calculate_footprint_size_amsu Calculate approximate footprint edge
0004 %
0005 % Calculates the semi-major axis, the semi-minor axis and the eccentricity of
0006 % an ellipse approximating the edge of the AMSU footprint, according to the
0007 % method found in bennartz00:_optim_convol_amsu_b_amsu_jaot, depending on the
0008 % scan position.
0009 %
0010 % FORMAT
0011 %
0012 %   [cross, along, eccentricity] = calculate_footprint_size_amsu(type, n)
0013 %
0014 % IN
0015 %
0016 %   type    string  'amsua' or 'amsub'
0017 %   n       scalar  channel number
0018 %
0019 % OUT
0020 %
0021 %   cross   scalar  cross-track size (km)
0022 %   along   scalar  along-track size (km)
0023 %   ecc     scalar  eccentricity for ellipse
0024 %
0025 % $Id: calculate_footprint_size_amsu.m 6679 2010-12-10 19:56:54Z gerrit $
0026         
0027 switch type
0028     case {'b', 'amsub'}
0029         if n > 45
0030             n = 91 - n;
0031         end
0032         cross = .5 * (79.08 + 2.84 * n - 14.78 * n^0.666);
0033         along = .5 * (28.72 - 0.90 * n + 0.094 * n^1.5);
0034 
0035     case {'a', 'amsua'}
0036         if n > 15
0037             n = 31 - n;
0038         end
0039 
0040         cross = .5 * (230.65 + 12.39 * n - 95.06 * n^0.5);
0041         along = .5 * (83.01 - 7.28 * n + 1.28 * n^1.5);
0042     otherwise
0043         error('atmlab:calculate_footprint_size_amsu', ...
0044             'Invalid sensor: %s', type)
0045 end
0046 
0047 a = max(cross, along);
0048 b = min(cross, along);
0049 
0050 eccentricity = sqrt(a.^2 - b.^2) / a;