How to change gregorian to julian?

My data is

time    
         Size:       1x1
         Dimensions: time
         Datatype:   single
         Attributes:
                     long_name     = 'Time'
                     standard_name = 'time'
                     units         = 'days since 1950-01-01 00:00:00 UTC'
                     calendar      = 'julian'
                     axis          = 'T'

How to change it to julian time? Thank you

Answer 1

[Meysam Mahooti]

%--------------------------------------------------------------------------
%
% Mjday: Modified Julian Date from calendar date and time
%
% Inputs:
%   year, month, day, hour, min, sec
%
% output:
%   Mjd    Modified Julian Date
%
% Last modified:   2015/08/12   M. Mahooti
%
%--------------------------------------------------------------------------
function Mjd = Mjday(year, month, day, hour, min, sec)

if (nargin < 4)
    hour = 0;
    min  = 0;
    sec  = 0;
end

y = year;
m = month;
b = 0;
c = 0;

if (m <= 2)
   y = y - 1;
   m = m + 12;
end

if (y < 0)
   c = -.75;
end

% check for valid calendar date
if (year < 1582)
   % null
elseif (year > 1582)
   a = fix(y / 100);
   b = 2 - a + floor(a / 4);
elseif (month < 10)
   % null
elseif (month > 10)
   a = fix(y / 100);
   b = 2 - a + floor(a / 4);
elseif (day <= 4)
   % null
elseif (day > 14)
   a = fix(y / 100);
   b = 2 - a + floor(a / 4);
else
    fprintf('\n\n  this is an invalid calendar date!!\n');
    return
end

jd = fix(365.25 * y + c) + fix(30.6001 * (m + 1));
jd = jd + day + b + 1720994.5;
jd = jd + (hour+min/60+sec/3600)/24;
Mjd = jd - 2400000.5;

https://www.mathworks.com/matlabcentral/fileexchange/55533-satellite-orbits--models--methods-and-applications

[min wong]

Thank you