get_nitrate.c

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#include <stdlib.h>
#include <math.h>
#include "l12_proto.h"
#include "get_nitrate.h"
 
/*
 *  Calculating Global and Basin Scale Maps of Sea surface Nitrate from Chlorophyll and SST using Empirical Algorithms.
 *  Modified by Joaquim Goes - 24 Aug 2017
 *  Implemented into l2gen by Robert Lossing May 2019
 */
 
float calc_nitrate(float chl, float sst, float lat, float lon) {
 
// Initiating Variables
 
    float no3;
    float nitrate = BAD_FLT;
 
    if (chl < 0) {
        return nitrate;
    }
 
    if (chl == BAD_FLT) {
        return nitrate;
    }
 
    no3 = 25.68 - 1.97 * sst + 0.04 * pow(sst, 2) - 1.63 * chl
            + 0.012 * pow(chl, 2);
 
// If Equatorial (Latitude: 30 degrees N and 18.33 degrees S):
 
    if (lat <= 30 && lat >= -18.333 && sst > 20 && chl > 0.24 && chl < 10) {
        no3 = 345.41 - 23.4 * sst + 0.4 * pow(sst, 2) + 0.012 * chl
                - pow(chl, 2) * 0.00048;
    }
 
// If Tropical Gyres:
 
    if (sst > 28 && chl >= 0.3 && chl <= 2) {
        no3 = 90.12 - 6.02 * sst + 0.09 * pow(sst, 2) - .05 * chl;
    }
 
// If Antartic (latitude) * and Arctic (latitude):
 
    if (sst < 2 && chl <= 2.2 && chl >= 0.1) {
        no3 = 12.98 - 13.61 * sst - 4.16 * pow(sst, 2) - 4.97 * chl
                + 0.267 * pow(chl, 2);
    }
 
// Condition 4 (Arabian Sea 45 degrees E and 86.666 E )
 
    if (lon >= 45 && lon <= 86.666 && lat <= 30 && lat >= 5) {
        no3 = 119.14 - 8.38 * sst + 0.15 * pow(sst, 2) - .2 * chl;
    }
 
// All other regions:
 
    nitrate = no3;
 
    if (nitrate < 0) {
        nitrate = 0;
    }
    if (nitrate > 40) {
        nitrate = 40;
    }
    return nitrate;
 
}
 
void get_nitrate(l2str *l2rec, l2prodstr *p, float prod[]) {
    int i;
    int16_t year, day;
    double sec;
    unix2yds(l2rec->l1rec->scantime, &year, &day, &sec);
 
    l1str *l1rec = l2rec->l1rec;
    l2rec->sst = get_sst(l2rec);
 
    for (i = 0; i < l1rec->npix; i++) {
        if (l2rec->chl[i] == BAD_FLT) {
            prod[i] = BAD_FLT;
            continue;
        }
 
        switch (p->cat_ix) {
 
        case CAT_nitrate:
            prod[i] = calc_nitrate(l2rec->chl[i], l2rec->sst[i], l1rec->lat[i], l1rec->lon[i]);
            break;
 
        default:
            printf("get_nitrate.c can not produce product %s\n",
                    p->algorithm_id);
            exit(1);
        }
 
        if (isnan(prod[i])) {
            prod[i] = BAD_FLT;
            l1rec->flags[i] |= PRODFAIL;
 
        }
    }
}