function his = read_HIS_record(file,index);
%
%       function his_record = read_HIS_record(file,fp,index);
%
%   ....This Matlab function reads one HIS record based on the file
%       pointer fp and the file index.
%
%       Written by Von P. Walden
%                  14 May 1998
%

fp = fopen(file);

% if filename is not specified, get from user
if nargin == 0 
  [fname,pname] = uigetfile('*.ume');
  file = [pname fname];
end
his.filename = file;

%
%   ....Skips to appropriate record and reads header and data.
%
fseek(fp,(index-1)*2150*4,'bof');
header = fread(fp,100,'float32');
data   = fread(fp,2050,'float32');

npts = header(31);

% grab the radiances
his.header = header;
his.rad = data(1:npts)';
clear data;

% define some specific header data
his.record_number = header(1);
his.channel_number = header(2);
his.mirror_position = header(3);
his.no_pts_in_ifgm = header(8);
his.seconds = header(11);
his.hbb_temp = header(12);
his.cbb_temp = header(13);
his.dc_ch1 = header(14);
his.dc_ch2 = header(15);
his.dc_ch3 = header(16);
his.year = header(17) + 1900;
his.month = header(18);
his.day = header(19);
his.bad_flag = header(20);
his.noise_flag = header(21);
his.std_phase = header(22);
his.begin_time = header(23);   % HHMMSS
his.current_time = header(24); % HHMMSS
his.qc_flag = header(25);      % 2 = spectrum o.k.
his.no_pts_in_fft = header(30);
his.no_pts_in_spectrum = header(31);
his.aircraft_lat = header(51);
his.aircraft_lon = header(52);
his.aircraft_alt = header(53);
his.aircraft_heading = header(54);

% Create frequency scale.
low = header(34);
high = header(35);
his.freq = linspace(low,high,npts);

% compute brightness temperatures
his.bt = real(rad2bt(his.freq,his.rad/1E3));

% define min, max wavenumbers for regions of good data
if his.channel_number(1) == 3
    his.wn1 = 600; his.wn2 = 1075;
  elseif his.channel_number(1) == 2
    his.wn1 = 1080;his.wn2=1800;
  elseif his.channel_number(1) == 1
    his.wn1 = 2050;his.wn2=2650;
end

% pull hour, minute, second from current_time (HHMMSS)
his.hour = fix(his.current_time/1e4);
his.minute = fix((his.current_time - 1e4*his.hour)/1e2);
his.second =  fix(his.current_time - his.hour*1e4 - his.minute*1e2);

% compute # seconds since 1970 (dont' ask why)
his.nss1970 = nosecsince1970(his.year,his.month,his.day,his.hour,his.minute,his.second);

% define wavenumber regions for radiance vs time
if his.channel_number(1) == 3
  his.wnbr1(1) = 898;his.wnbr2(1) = 904;
  his.wnbr1(2) = 700;his.wnbr2(2) = 710;
elseif his.channel_number(1) == 2
  his.wnbr1(1) = 1124;his.wnbr2(1) = 1132;
  his.wnbr1(2) = 1582;his.wnbr2(2) = 1588;
elseif his.channel_number(1) == 1
  his.wnbr1(1) = 2384;his.wnbr2(1) = 2392;
  his.wnbr1(2) = 2460;his.wnbr2(2) = 2470;
end

fclose(fp);