function OUT = prc_lu0(IN)
% PRC_LU0 - Estimate LU(0+)
%
% PRC_LU0 estimates the upwelled radiance across the air-water interface (Lu(0+)) 
% for 412 (nm), 443, 510, 555, 670, and 683. The relationships between radiances are
% dervied from linear regressions of data from the equatorial pacific near local noon.
% Contact Peter Strutton for details on the methods.
%
% Currently this requires that we do some prerocessing of the data using prc_ed490
% PRC_LU0 and PRC_ED490 will be combined at a later date.
%
% Use as: OUT = prc_lu0(IN)
% Inputs: IN = Data structure created by READOUT
% Output: OUT = Data structure with all fields in IN and the following additional fields:
%               LU0_412, LU0_443, LU0_510, LU0_555, LU0_670, LU0_683, 
%               LUWN_412, LUWN_443, LUWN_510, LUWN_555, LUWN_670, and LUWN_683

% Brian Schlining
% 20 Jan 1999

% Lu0+ are the radiances just above the air water interface
IN.LU0_412 = 0.557   .* IN.LU_412 + 0.014;
IN.LU0_443 = 0.559   .* IN.LU_443 + 0.012;
IN.LU0_490 = 0.563   .* IN.LU_490 + 0.003;
IN.LU0_510 = 0.578   .* IN.LU_510 - 0.002;
IN.LU0_555 = 0.601   .* IN.LU_555 - 0.002;
IN.LU0_670 = 0.671   .* IN.LU_670 - 0.001;
IN.LU0_683 = 0.590   .* IN.LU_683 + 0.001;

% Set negative values to NaN
%i = find(IN.LU0_412 < 0);IN.LU0_412(i) = NaN;
%i = find(IN.LU0_443 < 0);IN.LU0_443(i) = NaN;
%i = find(IN.LU0_490 < 0);IN.LU0_490(i) = NaN;
%i = find(IN.LU0_510 < 0);IN.LU0_510(i) = NaN;
%i = find(IN.LU0_555 < 0);IN.LU0_555(i) = NaN;
%i = find(IN.LU0_670 < 0);IN.LU0_670(i) = NaN;
%i = find(IN.LU0_683 < 0);IN.LU0_683(i) = NaN;



% Normalized water leaving radiances
IN.LUWN_412 = IN.LU0_412./IN.ED_412;
IN.LUWN_443 = IN.LU0_443./IN.ED_443;
IN.LUWN_490 = IN.LU0_490./IN.ED_490;
IN.LUWN_510 = IN.LU0_510./IN.ED_510;
IN.LUWN_555 = IN.LU0_555./IN.ED_555;
IN.LUWN_670 = IN.LU0_670./IN.ED_656;
IN.LUWN_683 = IN.LU0_683./IN.ED_683;

% Set negative values to NaN
%i = find(IN.LUWN_412 < 0);IN.LUWN_412(i) = NaN;
%i = find(IN.LUWN_443 < 0);IN.LUWN_443(i) = NaN;
%i = find(IN.LUWN_490 < 0);IN.LUWN_490(i) = NaN;
%i = find(IN.LUWN_510 < 0);IN.LUWN_510(i) = NaN;
%i = find(IN.LUWN_555 < 0);IN.LUWN_555(i) = NaN;
%i = find(IN.LUWN_670 < 0);IN.LUWN_670(i) = NaN;
%i = find(IN.LUWN_683 < 0);IN.LUWN_683(i) = NaN;

OUT = IN;