snotel_rain.c

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/*  possible error returns
 
     stn_values -    structure of inum reports
     inum -   number of reports          
     tstart - starting time
     tstop  - ending time
     maxgap - maximum data gap
     r->maxtdif- maximum time gap 
     r      - rain structure 
      r->rn -  amount of rain
      r->tdif- time gap of end time and last report
 
    error returns
     1 good data
    -1 no report after begin time
    -2 no report after end time
    -3 time gap between begin time and first report after begin time too large
    -4 data not reliable
    -5 large gaps in data
 
    
                                                                 */
 
#include "prototypes.h"
 
int snotel_rain(struct stn_values *stn_values,int inum,
           time_t tstart,time_t tstop,struct rainfall *r)
 
 
{
 
int j,maxhours,eflag,sindex;
double fdif,mindif,pdif,svalue;
long tdif;
 
r->rn=0.0;
r->rel=0;
r->obs=0;
r->tskips=0;
r->tdif=0L;
fdif=0.0;
mindif=.2;
maxhours=96;
eflag=-1;
 
for(j=0;j<inum;j++) {
 
         /* observation time before start time */
 
                sindex=j;
                if(j > 0 && (stn_values[j-1].value  -  stn_values[j].value) > 0.0) {
                   fdif=weigh(stn_values,j,inum,pdif,mindif,maxhours,&sindex,&svalue);
 
                                                                    }
                if(stn_values[j].clock > tstart) 
                                      continue;
 
                if(j==0 && (tstart - stn_values[j].clock) > r->firstdif) {         
 
                                                  r->tdif=tstart-stn_values[j].clock;
                                                  return(-3);
 
                                                                           }
                if(r->obs==0 && (tstart - stn_values[j].clock) > r->firstdif) {         
 
                                                  r->tdif=tstart-stn_values[j].clock;
                                                  return(-3);
 
                                                                           }
 
                if(j > 0) {
 
                          tdif=stn_values[j-1].clock -  stn_values[j].clock;
                          pdif=stn_values[j-1].value  -  stn_values[j].value;
                   
 
                          if(pdif > 0.0)
                               fdif=weigh(stn_values,j,inum,pdif,mindif,maxhours,&sindex,&svalue);
 
                          else
                               fdif=0.0;
 
                          }
 
                if(stn_values[j].clock < tstop)  {
 
                         if(fdif <= 0)
                                  return(1);
 
                         if((tstop - stn_values[j].clock) > r->firstdif)         
                                      return(-1);
 
                         if( fdif >= r->maxgap*2) 
                                            return(-5);
 
 
                         r->rn=r->rn+fdif/tdif*(stn_values[j-1].clock-tstop);
/*
                         r->rn=r->rn+fdif;        
*/
                         return(1);
 
                                         }
 
                r->obs++;
                eflag=-2;
 
                if(r->obs <= 1)     
                            continue;
 
                if(tdif > r->maxtdif && fdif != 0) 
                                         r->tskips++;
 
                if(fdif < 0)
                          continue;
 
                if( fdif >= r->maxgap*2) {
 
                                     r->rel++;
                                     if(r->rel >= 2)
                                                 eflag=-4;
 
                                       }
 
               else 
                      r->rn=r->rn+fdif;        
 
 
                       }
return(eflag);
 
}