get_ascend_decend_node

% get_ascend_decend_node Gets ascending/dedcending node
 Purpose: Create a logical array, the same size as latitude -matrix that
 indicates whether a pixel is in the ascending mode containing whether a pixel
 is ascending or not. 

 FORMAT:  ascend = get_ascend_decend_node(latitude)

 IN: Latitude (ungridded (size = [scanline,scanposition]))

 OUT: ascend (logical). true for ascend, false for descend.
 
 Note: 1) Latitude must have the dimensions size = [scanline,scanposition]
       2) This is for ungridded data. I.e. the latitude-matrix is a matrix (or
          vector) read straight from a satellite data file (therfore ungridded)
       3) If there is only one latitude scanline or if it's empty, ascend = NaN
       4) The node is based on the centre scanposition, i.e for amsub column
          45, for CloudSat column 1. That means that the entire scanline will
          always have the same node

 2010-10-13 created by Salomon Eliasson

0001 function ascend = get_ascend_decend_node(latitude)
0002 %% get_ascend_decend_node Gets ascending/dedcending node
0003 % Purpose: Create a logical array, the same size as latitude -matrix that
0004 % indicates whether a pixel is in the ascending mode containing whether a pixel
0005 % is ascending or not.
0006 %
0007 % FORMAT:  ascend = get_ascend_decend_node(latitude)
0008 %
0009 % IN: Latitude (ungridded (size = [scanline,scanposition]))
0010 %
0011 % OUT: ascend (logical). true for ascend, false for descend.
0012 %
0013 % Note: 1) Latitude must have the dimensions size = [scanline,scanposition]
0014 %       2) This is for ungridded data. I.e. the latitude-matrix is a matrix (or
0015 %          vector) read straight from a satellite data file (therfore ungridded)
0016 %       3) If there is only one latitude scanline or if it's empty, ascend = NaN
0017 %       4) The node is based on the centre scanposition, i.e for amsub column
0018 %          45, for CloudSat column 1. That means that the entire scanline will
0019 %          always have the same node
0020 %
0021 % 2010-10-13 created by Salomon Eliasson
0022 
0023 lat=latitude(:,round(end/2)); %always a vector
0024 ascend=false(size(latitude));
0025 
0026 if size(latitude,1)<=1
0027     ascend = NaN;
0028     return
0029 end
0030 
0031 % this line checks if the next latitude is higher or not (using indexing).
0032 % the second last and last scanlines are set to be equally ascending or
0033 % descending to their neighbouring point
0034 i = 1:length(lat)-1;
0035 ascend(i,:)=repmat(lat(i+1) > lat(i),1,size(ascend,2));
0036 ascend(end,:) = ascend(end-1,:);