c_daynite - Calculate the solar zenith angle at a point within the pass. The solar zenith angle is then used to determine if the image is a day or night pass.

SYNTAX

FUNCTION c_daynite (jdate, year, tsec, plat, plong, sunzen, dayn)

    long *jdate;
    long *year;
    double *tsec;
    double *plat;
    double *plong;
    double *sunzen;
    long *dayn;

PARAMETERS

jdate (long *, input)

The julian date of the pass.

year (long *, input)

The year of the pass (ie. 94 for 1994).

tsec (double *, input)

The time at the point specified by plat and plong. This time specifies total seconds since midnight GMT.

plat (double *, input)

The latitude of the point within the scene.

plong (double *, input)

The longitude of the point within the scene.

sunzen (double *, output)

The computed solar zenith angle.

dayn (long *, output)

The day/night indicator:

     =  1:	Day pass
     = -1:	Night pass

DESCRIPTION

Given the date, time, and location within a scene, c_daynite() calculates the solar zenith angle at this location and determines if the image is a day or night pass (a solar zenith angle between zero and ninety degrees constitutes a day pass).

RETURN VALUE

c_daynite() has no return value.