U.S. Geological Survey Open File Report OF-93-722

Appendix D. MATLAB Script File for BASS Calibration

%function [cal_cms_in, bass_cms_out, fit_err, calc_factor] = 

%    basscal(bass_count, cal_ns_in, avgint, offset, file);

%

%       display the results from a bass calibration with 

%           least squares fit, compute the conversion factor for 

%			each calibration data point, plot the results.

%       bass_count = bass raw data in counts, a cumulative sum of

%			samples collected over the given average interval avgint

%       cal_ns_in = calibrator's ns delay input to BASS

%       avgint = number of samples per data point

%	    offset = ns delay offset applied to zero the output at start

%	    file = filename in which to save text output

%       cal_cms_in = calibrator's delay input in cm/s 

%		bass_cms_out = cm/s computed from the BASS output

%       fit_err = error from a linear fit to the BASS output

%       calc_factor = the count to cm/s conversion factor based on each data point

%



% Written by Marinna Martini for the

% U.S. Geological Survey, Woods Hole, MA



function [fit_err, calc_factor] = ...

    basscal(bass_count, cal_ns_in, avgint, offset, file);

if exist('avgint') ~= 1,

        avgint = 1;     % assume no averaging

end

% ---- account for the offset

if exist('offset') ~= 1, offset = 0; end



% ---- convert to real units

Factor = 0.03;          % 0.03 cm/s per count

bass_cms=(bass_count./avgint).*Factor;	% BASS normalized using generic factor

cal_cms_in=cal_ns_in.*0.75;		% 0.75 cm/s per ns

calc_factor=cal_cms_in./(bass_count./avgint);



% ---- liner fit

l=length(bass_count);

c = polyfit(cal_ns_in, bass_cms,1);

fit_cms = polyval(c, cal_ns_in);



clf

% *********************** upper plot **************************

ptr=axes('Position',[0.15 0.1 0.8 0.6]);

% ---- display fit and data points

plot(cal_ns_in,bass_cms,'x',cal_ns_in,fit_cms,'-',cal_ns_in,cal_cms_in,'--');

grid

if mean(bass_cms) > 0,

	set(ptr,'ylim',[0 120],'xlim',[0 160]);

else

	set(ptr,'ylim',[-120 0],'xlim',[-160 0]);

end

%title('BASS Calibration Linearity Check')

text('units','normalized','position',[0.01 0.85],'string','--- least squares fit')

text('units','normalized','position',[0.01 0.90],'string',' X  BASS output')

text('units','normalized','position',[0.01 0.95],'string','- - Calibrator Input')

xlabel('Nanosecond Delay')

ylabel('cm/s')

fit_err=fit_cms-bass_cms;

txt=sprintf('mean(calibrator-BASS) = %7.4f',mean(cal_cms_in-bass_cms));

text('units','normalized','position',[0.5 0.05],'string',txt)

txt=sprintf('fit error: std = %7.4f',std(fit_err));

text('units','normalized','position',[0.6 0.1],'string',txt)



% *********************** lower plot *************************

ptr=axes('Position',[0.15 0.725 0.8 0.15]);

% ---- plot different in cm/s

plot(cal_ns_in,calc_factor,'-');

if mean(bass_cms) > 0,

	set(ptr,'ylim',[0.028 0.032 ],'xlim',[0 160]);

else

	set(ptr,'ylim',[0.028 0.032],'xlim',[-160 0]);

end

ylabel('cm/s per count')

set(ptr,'xtick',[]);

text('units','normalized','position',[0.01 1.1],'string',...

	'Conversion factor computed from calibration data');

grid

text('units','normalized','position',[0.45 1.5],...

	'HorizontalAlignment','center',...

	'string',['BASS: Linearity Check ',date]);

%

% ------- Generate Text Report

%

if exist('file') == 1,	% user wants output

	if exist(file) >= 2,	% file already exists

		disp([file ' already exists.  Saving to basscal.out'])

		file='basscal.out';

        delete basscal.out,

    end

    eval(['diary ' file])

end

fprintf ('\n')

fprintf('   BASS Calibration %s\n', date)

fprintf('\n')

fprintf('Delay Input\tOut: BASS, Fit\tError  Factor\n')

fprintf('ns\tcm/s\tcm/s\tcm/s\tcm/s\tcm/s per count\n')

for j=1:l,

    fprintf('%04.1f\t%04.1f\t%6.3f\t%6.3f\t%5.3f\t%6.4f\n', cal_ns_in(j),...

	cal_cms_in(j), bass_cms(j), fit_cms(j), fit_err(j), calc_factor(j));

end

fprintf('\nOffset applied to zero BASS output: %4.2f ns\n',offset);

fprintf('Number of samples averaged per calibration point: %3.0f\n',avgint);

fprintf('Mean(calibrator-BASS) = %7.4f cms\n',mean(cal_cms_in-bass_cms));

fprintf('Fit error: std = %7.4f cms\n',std(fit_err));

if exist('file') == 1,

    diary off

end