A DC9 CREW AT RIC ELECTS TO ABANDON THEIR APCH ABOVE MINIMUMS DUE TO THE WX CONDITIONS AND THEIR PERCEPTION OF THE LIMITATIONS OF THE ONBOARD RADAR.

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FO WAS FLYING THE ILS RWY 16 TO RIC. RAIN SHOWERS AND TSTMS WERE N AND W OF THE FIELD. THE AUTOPLT WAS COUPLED TO THE ILS FOR THIS APCH. ALTHOUGH THE RPTED WX CONDITIONS APPEARED TO BE EVEN A VISUAL APCH; THE FULL ILS WAS NEEDED DUE TO THE FLT CONDITIONS AND HVY RAIN AT OUR POS ON THE FINAL APCH SEGMENT. THE INTERCEPT AND FLYING OF THE APCH WERE UNEVENTFUL UNTIL THE RAIN WAS TOO HVY TO ADEQUATELY SEE THE RWY ENVIRONMENT. AIRSPD CTL WAS A LITTLE DIFFICULT BUT NOT UNMANAGEABLE. AFTER INTERCEPTING THE GS AND PROCEEDING WITH THE REST OF THE APCH WE OBTAINED SIGHT OF THE RWY LIGHTS AT APPROX 1000 FT AGL. AT APPROX 200 FT PRIOR TO MINIMUMS THE RWY LIGHTS BECAME VERY DIFFICULT TO SEE (EVEN AT A FULL BRIGHTNESS SETTING). I INSTRUCTED THE FO THAT IF HE FELT UNCOMFORTABLE AT ALL WITH THE APCH; AS IT WAS PROGRESSING; TO FEEL FREE TO GO AROUND EARLY. THE FO STATED THAT HE HAD LOST SIGHT OF THE RWY LIGHTS. WE ELECTED TO EXECUTE A MISSED APCH 200 FT PRIOR TO THE DECISION ALT. WE WERE GIVEN VECTORS FOR ANOTHER ILS APCH TO RWY 16 AND LANDED UNEVENTFULLY. ALTHOUGH WE COULD HAVE FLOWN THE ACFT TO THE DECISION ALT; THEN ELECTED TO EXECUTE THE MISSED APCH PROC; THE RAPIDLY DETERIORATING VISIBILITY CAUSED BY HVY RAIN AND THE ABILITY TO CTL THE AIRSPD MADE OUR EARLY DECISION THE PRUDENT COURSE OF ACTION. AGGRAVATING THE WORKLOAD IN THIS SCENARIO WAS THE DIFFICULTY IN INTERPRETING THE RADAR DISPLAY. AFTER FLYING WITH THIS TYPE RADAR A FEW TIMES I HAVE NOTICED THAT WHAT MAY APPEAR TO BE HVY PRECIPITATION ACTUALLY ISN'T. SIMPLY PUT; JUST ABOUT ANY PRECIPITATION LEVEL ABOVE A VERY LIGHT INTENSITY APPEARS TO BE RED. THIS MAKES PLANNING A FLT PATH AROUND EMBEDDED TSTMS VERY DIFFICULT BECAUSE THE CREW HAS NO WAY OF KNOWING WHAT WOULD BE THE SAFEST RTE. CAREFUL MANIPULATION OF THE GAIN SETTING HAS HELPED WITH THE DISPLAY. THIS TECHNIQUE HAS BEEN DEVELOPED ONLY AFTER ACTUAL EXPERIENCE WITH ENCOUNTERING A RED AREA (AS DISPLAYED ON THE RADAR) WHEN IT IS ACTUALLY A VERY LIGHT RAIN. ADJUSTING THE GAIN ISN'T VERY PROBLEMATIC AT CRUISE ALT BUT CAN BE A SOURCE OF ADDITIONAL WORKLOAD AND IRRITATION DURING THE APCH; AND THEREBY FRUSTRATING THE CREW'S ANALYSIS OF SIT. SHOULD A CREW ELECT TO ABORT AN APCH TO AN ARPT OR DIVERT DUE TO HVY PRECIPITATION OR TSTM WHICH REALLY ISN'T THERE; ALL THAT HAS HAPPENED IS THAT THE PIC HAS ERRED TOWARD THE CONSERVATIVE COURSE OF ACTION. THE QUESTION REMAINS; WHAT OF A CREW THAT MAY HAVE THE GAIN SETTING TOO LOW; OR IGNORES THE RED AREA OF THE DISPLAY THINKING IT IS ONLY LIGHT PRECIPITATION WHEN IN REALITY IT IS A TSTM OR AREA OF SEVERE TURB?