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:

Level-2 soil moisture product (SPL2SMP)

Level-3 soil moisture product (SPL3SMP)

Level-2 enhanced soil moisture product (SPL2SMP_E)

Level-3 enhanced soil moisture product (SPL3SMP_E)

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