So just change it back to forward slashes. I tried this and it worked
fine:
fname = 'HELENA/A-HMC180.at2';
[pathstr, name, ext] = fileparts(fname)
ext = '.AT2';
fname_url = fullfile(pathstr,[name ext])
initial = 'http://peer.berkeley.edu/nga_files/ath/'
site = fullfile('http://peer.berkeley.edu/nga_files/ath/', fname_url)
% Now change \ back to /
site = strrep(site, '\', '/')
record_URL1 = urlread(site)
fine:
fname = 'HELENA/A-HMC180.at2';
[pathstr, name, ext] = fileparts(fname)
ext = '.AT2';
fname_url = fullfile(pathstr,[name ext])
initial = 'http://peer.berkeley.edu/nga_files/ath/'
site = fullfile('http://peer.berkeley.edu/nga_files/ath/', fname_url)
% Now change \ back to /
site = strrep(site, '\', '/')
record_URL1 = urlread(site)