How do I interpret the surface and quality flag information in the Level-2 and -3 passive soil moisture products?
SMAP data files contain rich quality information that can be useful for many data users. The retrieval quality flag and surface flag bit values and interpretations are documented in the respective product Data Fields pages of the user guides for these data products
Level-2 soil moisture product (SPL2SMP)
- spl2smp#retrieval_qual_flag
- spl2smp#surface_flag
Level-3 soil moisture product (SPL3SMP)
- spl3smp#retrieval-qual-flag
- spl3smp#surface-flag
Level-2 enhanced soil moisture product (SPL2SMP_E)
- spl2smp_e#retrieval_qual_flag
- spl2smp_e#surface_flag
Level-3 enhanced soil moisture product (SPL3SMP_E)
- spl3smp_e#retrieval-qual-flag
- spl3smp_e#surface-flag
The tables below provide more detail and examples illustrating the relationship between the surface flag and the retrieval quality flag.
Table 1. If/Then Statements
If statement | Quality meaning | Then statement |
|---|---|---|
If surface_flag bit N = 0 | A. Recommended quality OR B. Uncertain quality AND C. Retrieval attempted | Then this bit “contributes” to the retrieval_qual_flag bit 0 = 0 (A) OR bit 0 = 1 (B) AND bit 1 = 0 (C) |
If surface_flag bit N = 1 | A. Retrieval skipped | Then this bit “contributes” to the retrieval_qual_flag bit 1 = 1 (A) |
If retrieval_qual_flag bit 0 = 0 AND bit 1 = 0 | Recommended quality AND Retrieval attempted | Then ALL surface_flag bits must = 0 AND ALL surface condition values are less than T1 |
If retrieval_qual_flag bit 0 = 1 AND bit 1 = 0 | Uncertain quality AND Retrieval attempted | Then ALL surface_flag bits must = 0 AND At least 1 surface condition value (of the 0 – 10 bits) must be between T1 and T2 |
If retrieval_qual_flag bit 1 = 1 | Retrieval skipped | Then at least 1 surface_flag bit must = 1 |
Table 2. Example using different possible values of the static water surface condition value
Scenarios | static water surface condition value | surface_flag bit 0 value | retrieval_qual_flag “contribution” | Actual possible retrieval_qual_flag | Notes |
|---|---|---|---|---|---|
Best scenario | 0.02 (less than T1) | 0 | Bit 0 = 0 AND Bit 1 = 0 | Best Bit 0 = 0 AND Bit 1 = 0
Good Bit 0 = 1 AND Bit 1 = 0
Bad Bit 0 = 1 AND Bit 1 = 1 | If any of the other surface_flag bits “contribute” anything other than this “best” scenario value, then the retrieval_qual_flag bits will be set according to the “worst” quality surface_flag. |
Good scenario | 0.07 (between T1 and T2) | 0 | Bit 0 = 1 AND Bit 1 = 0 | Good Bit 0 = 1 AND Bit 1 = 0
Bad Bit 0 = 1 AND Bit 1 = 1 |
|
Bad | 0.11 (greater than T2) | 1 | Bit 0 = 1 AND Bit 1 = 1 | Bad Bit 0 = 1 AND Bit 1 = 1 | Even if all other 10 surface_flag bits are “good” quality, the retrieval_qual_flag will be set as such |
Last Updated April 2017