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/*-------------------------------------------------------------------- |
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* $Id: sun.c,v 1.6 2004/07/05 06:57:56 pa2h Exp $ |
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* |
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* This file is part of libRadtran. |
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* Copyright (c) 1997-2001 by Arve Kylling and Bernhard Mayer. |
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* |
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* ######### Contact info: http://www.libradtran.org ######### |
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* |
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* This program is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU General Public License |
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* as published by the Free Software Foundation; either version 2 |
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* of the License, or (at your option) any later version. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place - Suite 330, |
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* Boston, MA 02111-1307, USA. |
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*--------------------------------------------------------------------*/ |
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|
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|
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/* sun.a - Solar zenith and azimuth calculations @ti@ */ |
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/* */ |
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/* Most of the formulas are adopted from: */ |
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/* Iqbal, Muhammad: "An Introduction to Solar Radiation", */ |
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/* Academic Press, Inc., 1983 */ |
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/* (page numbers in the comments refer to this book). */ |
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/* */ |
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/* Time is specified in seconds from midnight, */ |
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/* angles are specified in degrees. */ |
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|
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#include <math.h> |
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#include <stdio.h> |
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#include <string.h> |
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#include "sun.h" |
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|
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|
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|
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/* @42c@ */ |
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/* @c42@ */ |
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/****************************************************************************/ |
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/* In order to use the functions provided by the sun library, @42_10c@ */ |
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/* #include <sun.h> in your source code and link with libRadtran_c.a. */ |
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/* */ |
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/* @strong{Example:} */ |
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/* Example for a source file: */ |
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/* @example */ |
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/* */ |
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/* ... */ |
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/* #include "../src_c/sun.h" */ |
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/* ... */ |
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/* */ |
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/* @end example */ |
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/* */ |
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/* Linking of the executable, using the GNU compiler gcc: */ |
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/* @example */ |
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/* */ |
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/* gcc -o test test.c -lRadtran_c -L../lib */ |
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/* */ |
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/* @end example @c42_10@ */ |
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/****************************************************************************/ |
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|
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|
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/****************************************************************************/ |
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/* The sun library provides functions for solar zenith and azimuth @42_20c@ */ |
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/* angle and sun-earth-distance calculations. All formulas have been taken */ |
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/* from Iqbal, "An introduction to solar radiation". */ |
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/* @c42_20@ */ |
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/****************************************************************************/ |
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|
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|
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/* define _PI_ */ |
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#define _PI_ 3.1415926 |
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|
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/* internal functions */ |
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static double dayangle (int day); |
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|
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|
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/***********************************************************************************/ |
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/* Function: dayangle */ |
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/* Description: */ |
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/* Internal function to calculate the dayangle according to Iqbal, pg. 3 */ |
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/* */ |
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/* Parameters: */ |
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/* int day: day of year. */ |
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/* */ |
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/* Return value: */ |
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/* double dayangle, 0..2pi */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
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/* Author: */ |
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/* */ |
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/***********************************************************************************/ |
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|
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static double dayangle (int day) |
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{ |
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return 2.0 * _PI_ * (double) (day-1) / 365.0; |
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} |
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: eccentricity @42_30i@ */ |
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/* Description: */ |
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/* Calculate the eccentricity correction factor E0 = (r0/r)**2 according to */ |
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/* Iqbal, page 3. This factor, when multiplied with the irradiance, accounts */ |
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/* for the annual variation of the sun-earth-distance. */ |
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/* */ |
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/* Parameters: */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* */ |
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/* Return value: */ |
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/* The eccentricity (double) for the specified day. */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
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/* Author: */ |
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/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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double eccentricity (int day) |
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{ |
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double E0=0, angle=0; |
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|
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angle = dayangle (day); |
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|
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E0 = 1.000110 + 0.034221 * cos(angle) + 0.001280 * sin(angle) |
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+ 0.000719 * cos(2*angle) + 0.000077 * sin(2*angle); |
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|
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return E0; |
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} |
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: declination @42_30i@ */ |
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/* Description: */ |
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/* Calculate the declination for a specified day (Iqbal, page 7). */ |
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/* */ |
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/* Parameters: */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* */ |
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/* Return value: */ |
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/* The declination in degrees (double) for the specified day. */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
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/* Author: */ |
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/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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double declination (int day) |
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{ |
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double delta=0, angle=0; |
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|
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angle = dayangle (day); |
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|
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delta = 0.006918 - 0.399912 * cos (angle) + 0.070257 * sin (angle) |
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- 0.006758 * cos (2*angle) + 0.000907 * sin (2*angle) |
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- 0.002697 * cos (3*angle) + 0.00148 * sin (3*angle); |
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|
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delta *= 180.0/_PI_; |
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|
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return delta; |
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} |
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: equation_of_time @42_30i@ */ |
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/* Description: */ |
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/* Calculate the equation of time for a specified day (Iqbal, page 11). */ |
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/* */ |
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/* Parameters: */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* */ |
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/* Return value: */ |
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/* The equation of time in seconds (double) for the specified day. */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
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/* Author: */ |
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/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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int equation_of_time (int day) |
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{ |
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double angle=0, et=0; |
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|
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angle = dayangle (day); |
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|
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et = (0.000075 + 0.001868 * cos(angle) - 0.032077 * sin(angle) |
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-0.014615 * cos(2*angle) - 0.04089 * sin(2*angle)) * 13750.8; |
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|
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return (int) (et+0.5); |
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} |
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: LAT @42_30i@ */ |
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/* Description: */ |
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/* Calculate the local apparent time for a given standard time and location. */ |
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/* */ |
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/* Parameters: */ |
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/* int time_std: Standard time [seconds since midnight]. */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* double longitude: Longitude [degrees] (West positive). */ |
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/* double long_std: Standard longitude [degrees]. */ |
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/* */ |
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/* Return value: */ |
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/* The local apparent time in seconds since midnight (double). */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
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/* Author: */ |
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/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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int LAT (int time_std, int day, double longitude, double long_std) |
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{ |
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int lat=0; |
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|
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lat = time_std + (int) (240.0 * (long_std-longitude)) |
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+ equation_of_time (day); |
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|
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return lat; |
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} |
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|
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|
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/************************************************/ |
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/* convert local apparent time to standard time */ |
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/************************************************/ |
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|
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int standard_time (int lat, int day, double longitude, double long_std) |
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{ |
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return lat - (int) (240.0 * (long_std-longitude)) - equation_of_time (day); |
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} |
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|
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|
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/****************************/ |
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/* hour angle omega; pg. 15 */ |
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/****************************/ |
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|
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double hour_angle (int time) |
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{ |
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double omega=0; |
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|
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omega = _PI_ * (1.0 - ((double) time) / 43200.0); |
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|
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omega *= 180.0/_PI_; |
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return omega; |
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} |
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: solar_zenith @42_30i@ */ |
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/* Description: */ |
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/* Calculate the solar zenith angle for a given time and location. */ |
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/* */ |
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/* Parameters: */ |
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/* int time: Standard time [seconds since midnight]. */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* double latitude: Latitude [degrees] (North positive). */ |
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/* double longitude: Longitude [degrees] (West positive). */ |
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/* double long_std: Standard longitude [degrees]. */ |
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/* */ |
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/* Return value: */ |
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/* The solar zenith angle [degrees]. */ |
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/* */ |
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/* Example: */ |
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/* Files: */ |
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/* Known bugs: */ |
| 285 |
/* Author: */ |
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/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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double solar_zenith (int time, int day, |
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double latitude, double longitude, double long_std) |
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{ |
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double theta=0, omega=0, delta=0, phi = latitude*_PI_/180.0; |
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int lat = LAT (time, day, longitude, long_std); |
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|
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delta = _PI_/180.0*declination (day); |
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omega = _PI_/180.0*hour_angle (lat); |
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|
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theta = acos(sin(delta) * sin(phi) + cos(delta) * cos(phi) * cos(omega)); |
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|
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theta *= (180.0/_PI_); /* convert to degrees */ |
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return theta; |
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} |
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|
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|
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|
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|
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/***********************************************************************************/ |
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/* Function: solar_azimuth @42_30i@ */ |
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/* Description: */ |
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/* Calculate the solar azimuth angle for a given time and location. */ |
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/* */ |
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/* Parameters: */ |
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/* int time: Standard time [seconds since midnight]. */ |
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/* int day: day of year (leap day is usually @strong{not} counted. */ |
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/* double latitude: Latitude [degrees] (North positive). */ |
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/* double longitude: Longitude [degrees] (West positive). */ |
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/* double long_std: Standard longitude [degrees]. */ |
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/* */ |
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/* Return value: */ |
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/* The solar azimuth angle [degrees]. */ |
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/* */ |
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/* Example: */ |
| 323 |
/* Files: */ |
| 324 |
/* Known bugs: */ |
| 325 |
/* Author: */ |
| 326 |
/* @i42_30@ */ |
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/***********************************************************************************/ |
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|
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double solar_azimuth (int time, int day, |
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double latitude, double longitude, double long_std) |
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{ |
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double theta=0, omega=0, delta=0, phi = latitude*_PI_/180.0, psi=0, cospsi=0; |
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int lat = LAT (time, day, longitude, long_std); |
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|
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delta = _PI_/180.0*declination (day); |
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omega = _PI_/180.0*hour_angle (lat); |
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theta = _PI_/180.0*solar_zenith (time, day, latitude, longitude, long_std); |
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|
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|
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cospsi = (cos(theta)*sin(phi) - sin(delta)) / sin(theta) / cos (phi); |
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/* allow tiny roundoff errors */ |
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if (cospsi>1.0 && cospsi<1.0+1e-6) |
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cospsi=1.0; |
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|
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if (cospsi<-1.0 && cospsi>-1.0-1e-6) |
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cospsi=-1.0; |
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|
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psi = -acos(cospsi); |
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|
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/* adjust sign */ |
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if (lat>43200 || lat<0) |
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psi=-psi; |
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|
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psi *= (180.0/_PI_); /* convert to degrees */ |
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|
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return psi; |
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} |
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|
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|
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|
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/***********************************************************************************/ |
| 362 |
/* Function: day_of_year @42_30i@ */ |
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/* Description: */ |
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/* Calculate the day of year for given date (leap days are not considered. */ |
| 365 |
/* */ |
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/* Parameters: */ |
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/* int day: Day of month (1..31). */ |
| 368 |
/* int month: Month (1..12). */ |
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/* */ |
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/* Return value: */ |
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/* The day of year (int); -1 if error. */ |
| 372 |
/* */ |
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/* Example: */ |
| 374 |
/* Files: */ |
| 375 |
/* Known bugs: */ |
| 376 |
/* Author: */ |
| 377 |
/* @i42_30@ */ |
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/***********************************************************************************/ |
| 379 |
|
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int day_of_year (int day, int month) |
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{ |
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char mon = 0; |
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int doy = -1; |
| 384 |
|
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if (month<1 || month > 12) |
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return (-1); |
| 387 |
|
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if (day<1 || day > 31) |
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return (-1); |
| 390 |
|
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mon = (char) month; |
| 392 |
|
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switch (mon) { |
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case 1: |
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doy = day + 0; |
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break; |
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case 2: |
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doy = day + 31; |
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break; |
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case 3: |
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doy = day + 59; |
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break; |
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case 4: |
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doy = day + 90; |
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break; |
| 406 |
case 5: |
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doy = day + 120; |
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break; |
| 409 |
case 6: |
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doy = day + 151; |
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break; |
| 412 |
case 7: |
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doy = day + 181; |
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break; |
| 415 |
case 8: |
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doy = day + 212; |
| 417 |
break; |
| 418 |
case 9: |
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doy = day + 243; |
| 420 |
break; |
| 421 |
case 10: |
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doy = day + 273; |
| 423 |
break; |
| 424 |
case 11: |
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doy = day + 304; |
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break; |
| 427 |
case 12: |
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doy = day + 334; |
| 429 |
break; |
| 430 |
default: |
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doy = -1; |
| 432 |
} |
| 433 |
|
| 434 |
return (doy); |
| 435 |
} |
| 436 |
|
| 437 |
|
| 438 |
|
| 439 |
|
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/**************************************************************************/ |
| 441 |
/* convert time to string */ |
| 442 |
/* memory for timestr must be allocated by programmer (at least 10 bytes) */ |
| 443 |
/**************************************************************************/ |
| 444 |
|
| 445 |
char *time2str (char *timestr, int hour, int min, int sec) |
| 446 |
{ |
| 447 |
char hourstr[3] = ""; |
| 448 |
char minstr[3] = ""; |
| 449 |
char secstr[3] = ""; |
| 450 |
|
| 451 |
strcpy (timestr, ""); |
| 452 |
|
| 453 |
if (hour<0 || hour>24) |
| 454 |
return NULL; |
| 455 |
|
| 456 |
if (min<0 || min>60) |
| 457 |
return NULL; |
| 458 |
|
| 459 |
if (sec<0 || sec>60) |
| 460 |
return NULL; |
| 461 |
|
| 462 |
|
| 463 |
|
| 464 |
if (hour<10) |
| 465 |
sprintf (hourstr, "0%d", hour); |
| 466 |
else |
| 467 |
sprintf (hourstr, "%d", hour); |
| 468 |
|
| 469 |
if (min<10) |
| 470 |
sprintf (minstr, "0%d", min); |
| 471 |
else |
| 472 |
sprintf (minstr, "%d", min); |
| 473 |
|
| 474 |
if (sec<10) |
| 475 |
sprintf (secstr, "0%d", sec); |
| 476 |
else |
| 477 |
sprintf (secstr, "%d", sec); |
| 478 |
|
| 479 |
sprintf (timestr, "%s:%s:%s", hourstr, minstr, secstr); |
| 480 |
|
| 481 |
return timestr; |
| 482 |
} |
| 483 |
|
| 484 |
|
| 485 |
|
| 486 |
|
| 487 |
/***********************************************************************************/ |
| 488 |
/* Function: zenith2time @42_30i@ */ |
| 489 |
/* Description: */ |
| 490 |
/* Calculate the times for a given solar zenith angle, day of year and location. */ |
| 491 |
/* */ |
| 492 |
/* Parameters: */ |
| 493 |
/* int day: day of year */ |
| 494 |
/* double zenith_angle: Solar zenith angle [degrees]. */ |
| 495 |
/* double latitude: Latitude [degrees] (North positive). */ |
| 496 |
/* double longitude: Longitude [degrees] (West positive). */ |
| 497 |
/* double long_std: Standard longitude [degrees]. */ |
| 498 |
/* int *time1: 1st time of occurence. */ |
| 499 |
/* int *time2: 2nd time of occurence. */ |
| 500 |
/* */ |
| 501 |
/* Return value: */ |
| 502 |
/* 0 if o.k., <0 if error. */ |
| 503 |
/* */ |
| 504 |
/* Example: */ |
| 505 |
/* Files: */ |
| 506 |
/* Known bugs: */ |
| 507 |
/* Author: */ |
| 508 |
/* @i42_30@ */ |
| 509 |
/***********************************************************************************/ |
| 510 |
|
| 511 |
int zenith2time (int day, |
| 512 |
double zenith_angle, |
| 513 |
double latitude, |
| 514 |
double longitude, |
| 515 |
double long_std, |
| 516 |
int *time1, |
| 517 |
int *time2) |
| 518 |
{ |
| 519 |
double delta = _PI_/180.0*declination (day); |
| 520 |
double phi = _PI_/180.0*latitude; |
| 521 |
double theta = _PI_/180.0*zenith_angle; |
| 522 |
double cos_omega = (cos(theta) - sin(delta)*sin(phi)) / |
| 523 |
cos(delta) / cos(phi); |
| 524 |
double omega1=0, omega2=0; |
| 525 |
int lat1=0, lat2=0; |
| 526 |
|
| 527 |
if (fabs(cos_omega) > 1.0) |
| 528 |
return ERROR_NO_ZENITH; |
| 529 |
|
| 530 |
omega1 = acos (cos_omega); |
| 531 |
omega2 = 0.0-omega1; |
| 532 |
|
| 533 |
lat1 = 43200*(1-omega1/_PI_); |
| 534 |
lat2 = 43200*(1-omega2/_PI_); |
| 535 |
|
| 536 |
*time1 = standard_time (lat1, day, longitude, long_std); |
| 537 |
*time2 = standard_time (lat2, day, longitude, long_std); |
| 538 |
|
| 539 |
return 0; |
| 540 |
} |
| 541 |
|
| 542 |
|
| 543 |
|
| 544 |
|
| 545 |
|
| 546 |
/***********************************************************************************/ |
| 547 |
/* Function: Gregorian2Julian @42_30i@ */ |
| 548 |
/* Description: */ |
| 549 |
/* Convert from Gregorian day (day, month, year) to Julian day (by the */ |
| 550 |
/* astronomical definition). This function, in combination with */ |
| 551 |
/* Julian2Gregorian() is very useful to answer questions like "which date is */ |
| 552 |
/* 666 days after December 31, 1999?" Algorithm from */ |
| 553 |
/* H.F. Fliegel and T.C. Van Flandern, "A Machine Algorithm for Processing */ |
| 554 |
/* Calendar Dates", Communications of the Association for Computing Machinery */ |
| 555 |
/* (CACM), Vol. 11, No. 10, 657, 1968. */ |
| 556 |
/* */ |
| 557 |
/* Parameters: */ |
| 558 |
/* int d: Day of month (1..31). */ |
| 559 |
/* int m: Month (1..12). */ |
| 560 |
/* int y: Year (attention: full year required, 1999 instead of 99) */ |
| 561 |
/* int *jd: The Julian day, to be calculated. */ |
| 562 |
/* */ |
| 563 |
/* Return value: */ |
| 564 |
/* 0 if o.k., <0 if error. */ |
| 565 |
/* */ |
| 566 |
/* Example: */ |
| 567 |
/* Files: */ |
| 568 |
/* Known bugs: */ |
| 569 |
/* Author: */ |
| 570 |
/* @i42_30@ */ |
| 571 |
/***********************************************************************************/ |
| 572 |
|
| 573 |
int Gregorian2Julian (int d, int m, int y, int *jd) |
| 574 |
{ |
| 575 |
char ystr[3]=""; |
| 576 |
|
| 577 |
/* reset output */ |
| 578 |
*jd =0; |
| 579 |
|
| 580 |
if (d<1||d>31) |
| 581 |
return -1; |
| 582 |
|
| 583 |
if (m<1||m>12) |
| 584 |
return -1; |
| 585 |
|
| 586 |
if (y>0&&y<100) { |
| 587 |
if (y<10) |
| 588 |
sprintf (ystr, "0%d", y); |
| 589 |
else |
| 590 |
sprintf (ystr, "%d", y); |
| 591 |
|
| 592 |
fprintf (stderr, "Warning: Gregorian2Julian() has been called for year %s\n", ystr); |
| 593 |
fprintf (stderr, "Maybe you meant 19%s or 20%s?\n", ystr, ystr); |
| 594 |
} |
| 595 |
|
| 596 |
|
| 597 |
*jd = (1461 * (y + 4800 + (m - 14) / 12)) / 4 + |
| 598 |
(367 * (m - 2 - 12 * ((m - 14) / 12))) / 12 - |
| 599 |
(3 * ((y + 4900 + (m - 14) / 12) / 100)) / 4 + d - 32075; |
| 600 |
|
| 601 |
return 0; /* if o.k. */ |
| 602 |
} |
| 603 |
|
| 604 |
|
| 605 |
|
| 606 |
/***********************************************************************************/ |
| 607 |
/* Function: Julian2Gregorian @42_30i@ */ |
| 608 |
/* Description: */ |
| 609 |
/* Convert from Julian day (by the astronomical definition) to Gregorian day */ |
| 610 |
/* (day, month, year) to . This function, in combination with */ |
| 611 |
/* Gregorian2Julian() is very useful to answer questions like "which date is */ |
| 612 |
/* 666 days after December 31, 1999?" Algorithm from */ |
| 613 |
/* H.F. Fliegel and T.C. Van Flandern, "A Machine Algorithm for Processing */ |
| 614 |
/* Calendar Dates", Communications of the Association for Computing Machinery */ |
| 615 |
/* (CACM), Vol. 11, No. 10, 657, 1968. */ |
| 616 |
/* */ |
| 617 |
/* Parameters: */ |
| 618 |
/* int *d: Day of month (1..31), to be calculated. */ |
| 619 |
/* int *m: Month (1..12), to be calculated. */ |
| 620 |
/* int *y: Year, to be calculated. */ |
| 621 |
/* int jd: The Julian day. */ |
| 622 |
/* */ |
| 623 |
/* Return value: */ |
| 624 |
/* 0 if o.k., <0 if error. */ |
| 625 |
/* */ |
| 626 |
/* Example: */ |
| 627 |
/* Files: */ |
| 628 |
/* Known bugs: */ |
| 629 |
/* Author: */ |
| 630 |
/* @i42_30@ */ |
| 631 |
/***********************************************************************************/ |
| 632 |
|
| 633 |
int Julian2Gregorian(int *d, int *m, int *y, int jd) |
| 634 |
{ |
| 635 |
int l=0, n=0, i=0, j=0; |
| 636 |
|
| 637 |
l = jd + 68569; |
| 638 |
n = ( 4 * l ) / 146097; |
| 639 |
l = l - ( 146097 * n + 3 ) / 4; |
| 640 |
i = ( 4000 * ( l + 1 ) ) / 1461001; |
| 641 |
l = l - ( 1461 * i ) / 4 + 31; |
| 642 |
j = ( 80 * l ) / 2447; |
| 643 |
*d = l - ( 2447 * j ) / 80; |
| 644 |
l = j / 11; |
| 645 |
*m = j + 2 - ( 12 * l ); |
| 646 |
*y = 100 * ( n - 49 ) + i + l; |
| 647 |
|
| 648 |
return 0; |
| 649 |
} |
| 650 |
|
| 651 |
|
| 652 |
/***********************************************************************************/ |
| 653 |
/* Function: location @42_30i@ */ |
| 654 |
/* Description: */ |
| 655 |
/* Return latitude, longitude, and standard longitude for a given location. */ |
| 656 |
/* */ |
| 657 |
/* Parameters: */ |
| 658 |
/* double *latitude: Latitude (North positive). */ |
| 659 |
/* double *longitude: Longitude (West positive). */ |
| 660 |
/* double *long_std: Standard longitude (West positive). */ |
| 661 |
/* char *location: String identifying the location. */ |
| 662 |
/* */ |
| 663 |
/* Return value: */ |
| 664 |
/* 0 if o.k., <0 if error. */ |
| 665 |
/* */ |
| 666 |
/* Example: */ |
| 667 |
/* Files: */ |
| 668 |
/* Known bugs: */ |
| 669 |
/* Author: */ |
| 670 |
/* @i42_30@ */ |
| 671 |
/***********************************************************************************/ |
| 672 |
|
| 673 |
int location (char *locstr, double *latitude, double *longitude, double *long_std) |
| 674 |
{ |
| 675 |
|
| 676 |
if (!strcasecmp(locstr, "ifu")) { |
| 677 |
*latitude = 47.48; |
| 678 |
*longitude = -11.07; |
| 679 |
*long_std = -15.00; |
| 680 |
|
| 681 |
return 0; |
| 682 |
} |
| 683 |
|
| 684 |
if (!strcasecmp(locstr, "dlrop")) { |
| 685 |
*latitude = 48.088; |
| 686 |
*longitude = -11.280; |
| 687 |
*long_std = -15.000; |
| 688 |
|
| 689 |
return 0; |
| 690 |
} |
| 691 |
|
| 692 |
|
| 693 |
return -1; |
| 694 |
} |
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