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%drift_corr.m
%This function calculates the drift in the gravimeter from day to day and
%from morning to evening, and returns corrected gravity values.
%input: gravity values, times (day, hour, minute), and data matrix of
%measurements done in the basecamp in each day's morning and evening.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


function g_drift_corr = drift_corr (g, day, hour, minute, base_camp_data_matrix) 

base_camp_g = base_camp_data_matrix(:, 2);
base_camp_hour = base_camp_data_matrix(:, 3);
base_camp_min = base_camp_data_matrix(:, 4) + base_camp_hour.*60;
%
%calculate the drift per minute within each day and the drift between days
%
for d= 1:(length(base_camp_data_matrix(:,1)))/2
    day_corr(d) = base_camp_g(d*2-1) - base_camp_g(1);
    slope(d) = (base_camp_g(d*2) - base_camp_g(d*2-1)) ./ ( (base_camp_min(d*2)-base_camp_min(d*2-1)));
end

%
%calculate the minute within a day from each station
%
minute_on_day = (hour.*60 + minute) - base_camp_min(day.*2-1);

%
%calculate the corrected gravity using the day's slope and day-to-day change
%
g_drift_corr = g - slope(day)'.*minute_on_day + day_corr(day)';


g_drift_corr = g ;