H-SAF Product Validation Report (PVR) PR-OBS-3

Products Validation Report, 30 May 2010 - PVR-03 (Product PR-OBS-3) Page 16
For accumulated precipitation, user requirements are unclear in terms of dependence on amount. We
have adopted a 5-class splitting for results presentation and a 10-subclass subdivision for working
purpose (see Fig. 09).
Class
1 2 3 4 5
< 8 mm 8 - 32 mm 32-64 mm 64-128 mm > 128 mm
Subclass 1 2 3 4 5 6 7 8 9 10
(mm) < 1 1 - 2 2 - 4 4 - 8 8 - 16 16 - 32 32 - 64 64 - 128 128 - 256 > 128
Fig. 09 - Classes and sub-classes for evaluating Accumulated Precipitation products.
Applicable to PR-OBS-5 and PR-ASS-1accumulated
The evaluation of the statistical scores split by precipitation classes allows to analyse the product
performances not only for precipitation mean values (light precipitation being the more frequent) but
also for higher value, the most interesting for Hydrology.
3.3 Definition of statistical scores
It is appropriate to deploy the definitions of the statistical scores utilised in H-SAF product validation
activities. Some apply to “continuous statistics”, some to “dichotomous statistics”. Although neither
rain gauges nor radar constitute a very accurate ground truth, we assume as “true” these observations,
thus the departures of satellite observations will be designated as “errors”
Scores for continuous statistics:
- Mean Error (ME) or Bias
- Standard Deviation (SD)
- Correlation Coefficient (CC)
- Root Mean Square Error (RMSE)
- Root Mean Square Error percent (RMSE %), used for precipitation since error grows with rate.
ME or
bias
1
N
N
k 1
(sat
k
truek
)
SD
1
N
N
k 1
sat
k
true
k
ME
2
N
k
k
k 1
CC with
N
N
2
2
sat
sat
sat
sat
k
k 1
1
true
true
k
true
true
N
1
sat sat k
and
N
k 1
N
1
true true k
;
N
k 1
RMSE
1
N
N
k 1
sat k
true k
2
RMSE %
1
N
N
k 1
sat
k
true
2
true k
k
2