I leave you an example:
close all
RGB=imread('negativo/drone_image.jpg');
BW = (RGB(:,:,1) >= 142 ) & (RGB(:,:,1) <= 178) & ...
(RGB(:,:,2) >= 93 ) & (RGB(:,:,2) <= 215) & ...
(RGB(:,:,3) >= 182 ) & (RGB(:,:,3) <= 226);
BW = imdilate(BW,strel('line',300,90));
BW = bwpropfilt(BW, 'MajorAxisLength', [500, 5262]);
imshowpair(RGB,BW,'montage')