Two contingency statistics, probability of detection (POD) and false alarm ratio (FAR), are used to measure the accuracy between CMPA and gauge observations. Each pair of hourly rainfall records from gauges and CMPA grids are classified as a Hit, Miss, or False (Table 2). Both POD and FAR are computed based on the count definition of Hit, Miss and False by Equations (4) and (5) (Ebert et al. 2007):
4
5where Nhit is the total count of hours when both gauge and CMPA observe rain, which is equal or larger than the rain rate threshold (P0 = 0.1 mm/h). Nmiss is the total count of hours when CMPA misses rain that is detected by the gauge. Nfalse is the total count of hours when CMPA detects rain that is not detected by the gauge.
Table 2
Contingency table for gauge and CMPA estimate (P0 = 0.1 mm/h)
| Gauge ≥ P0 | Gauge < P0 | |
|---|---|---|
| CMPA ≥ P0 | Hit | False |
| CMPA < P0 | Miss | Null |
| Gauge ≥ P0 | Gauge < P0 | |
|---|---|---|
| CMPA ≥ P0 | Hit | False |
| CMPA < P0 | Miss | Null |