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stratiedSampleHanlder.m
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stratiedSampleHanlder.m
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function samples_ids=stratiedSampleHanlder(data_dem_clear,dem_b,dem_t,dim,total_sample,ele_strata,distance,resolution)
%STRATIEDSAMPLEHANLDER Further select clear sky (land) pixels to normalize
%BT.
%
% Syntax
%
% samples_ids=
% stratiedSampleHanlder(data_dem_clear,dem_b,dem_t,dim,total_sample,ele_strata,distance)
%
% Description
%
% Stratied sampling method is used by Qiu et al., (2017).
% History:
% 1. Create this function. (1. January, 2017)
% 2. This stratied sampling method sometimes results in no enough
% samples. (8. March, 2018)
%
% Input arguments
%
% data_dem_clear Clear sky pixels' DEM.
% dem_b Basic elevation.
% dem_t Highest elevation.
% dim Dim for data.
% total_sample All clear sky samples (40,000).
% ele_strata Stratied sampling along elevation (300 meters).
% distance Minmum distance among different samples(450 meters).
% Distance rule will be removed if distance = 0.
% resolution Spatial resolution (Landsat 30 meters; Sentinel-2 20 meters).
% Output arguments
%
% Tempd Nomalized Temperature (BT).
%
%
% Author: Shi Qiu (shi.qiu@uconn.edu)
% Date: 27. Jan, 2022
% set static seed for random generator. By Shi, at 27 Jan., 2022
%
% % num_clear_sky_pixels=numel(data_dem_clear);
% % % no enough clear-sky pixels afther removing the pixels out of the upper
% % % and lower levels.more than 1/4 total samples (10,000) can be used for
% % % estimating lapse rate and c in topo correction.
% % if num_clear_sky_pixels<total_sample/4
% % samples_ids=1:num_clear_sky_pixels;
% % return;
% % end
samp_dis= round(distance/resolution); % 450 m(15 30 m pixels)
clear distance resolution;
% compute the number of available strata
strata_avail=[];
for i_dem=dem_b:ele_strata:dem_t
dem_clear_index_tmp=data_dem_clear>=i_dem&data_dem_clear<i_dem+ele_strata;
if sum(dem_clear_index_tmp)>0
% num_strata=num_strata+1;
strata_avail=[strata_avail;1];
else
strata_avail=[strata_avail;0];
end
clear dem_clear_index_tmp;
end
% equal samples in each stratum
num_sam_each_strata=round(total_sample/sum(strata_avail));
clear total_sample;
samples_ids=[];% to restore samples selected.
% loop each strata and select samples
loop_i=1;
for i_dem=dem_b:ele_strata:dem_t
if strata_avail(loop_i)
% dem_clear_index_tmp=data_dem_clear>=i_dem&data_dem_clear<i_dem+ele_strata;
% find all clear-sky pixels in subgroup.
samples_ids_tmp=find(data_dem_clear>=i_dem&data_dem_clear<i_dem+ele_strata);
% randomly selection.
rng(1);% static seed
samples_ids_rand=samples_ids_tmp(randperm(numel(samples_ids_tmp)));
clear samples_ids_tmp;
num_tmp=size(samples_ids_rand,1);
if samp_dis==0 % no distance rule
num_max_tmp=num_sam_each_strata;
if num_tmp>num_max_tmp
num_tmp=num_max_tmp;
end
clear num_max_tmp;
samples_ids_rand_tmp=samples_ids_rand(1:num_tmp);
clear num_tmp;
% store data
samples_ids=[samples_ids;samples_ids_rand_tmp];
clear samples_ids_rand samples_ids_rand_tmp;
else
num_max_tmp=num_sam_each_strata*samp_dis;
if num_tmp>num_max_tmp
num_tmp=num_max_tmp;
end
clear num_max_tmp;
samples_ids_rand_tmp=samples_ids_rand(1:num_tmp);
clear num_tmp;
samples_ids_rand=samples_ids_rand_tmp;
clear samples_ids_rand_tmp;
all_num_tmp=size(samples_ids_rand);
[i_tmp,j_tmp]=ind2sub(dim,samples_ids_rand);
ij_tmp=[i_tmp,j_tmp];
clear i_tmp j_tmp;
% removing the clear-sky pixels of which distance lt 15.
idx_lt15 = rangesearch(ij_tmp,ij_tmp,samp_dis, 'distance','cityblock');
recorder_tmp=zeros(all_num_tmp,'uint8')+1;
for i_idx=1:all_num_tmp
if recorder_tmp(i_idx)>0 % when this label is available.
recorder_tmp(cell2mat(idx_lt15(i_idx)))=0;
recorder_tmp(i_idx)=1;% reback the current label as 1.
end
end
clear all_num_tmp idx_lt15;
idx_used=find(recorder_tmp==1);
clear recorder_tmp;
num_tmp=size(idx_used,1);
num_max_tmp=num_sam_each_strata;
if num_tmp>num_max_tmp
num_tmp=num_max_tmp;
end
idx_used=idx_used(1:num_tmp);
clear num_tmp num_max_tmp;
% store data
samples_ids=[samples_ids;samples_ids_rand(idx_used)];
clear samples_ids_rand idx_used;
end
end
loop_i=loop_i+1;
end
clear samp_dis num_sam_each_strata;
% % % no enough clear-sky pixels afther removing the pixels out of the upper
% % % and lower levels.more than 1/4 total samples (10,000) can be used for
% % % estimating lapse rate and c in topo correction.
% % if numel(samples_ids)<total_sample/4
% % samples_ids=1:num_clear_sky_pixels;
% % return;
% % end
end