Crop/No-Crop Samples for the Validation of Cropland Map in South Asia

Crop/No-Crop Samples for the validation of cropland map in South Asia

Summary:

1. 1591 samples generated blindly by 3 interpreters

2. Sampling scheme: Gridded random (i.e. systematic sampling) with 0.5x0.5 degree (Fig.2)

3. Samples were visually interpreted within a 250x250 homogeneous window

4. Interpretation Consensus on Reference Labels (Fig.3):

a. Cropland/Settlements

b. Cropland/Plantation

c. Cropland/Shrub land

5. Generated for accuracy assessment of 30m Cropland map of South Asia

6. 1500 independent samples can be generated for independent interpretation

Questions:

1. How were the samples distributed in a gridded pattern (e.g. center of a grid)?

Answer: The samples have been selected on the corners of a 0.5x0.5 degree grid. In other

words, the samples are on the corners of a 56x56km polygon. All the reference sample

polygons might not be falling in a 250x250m homogeneous area. Thus, the samples will

be checked once again if they are falling in homogeneous areas or not. The non-

homogeneous samples will be moved to the center of a nearby 250x250m homogeneous area in any direction (See Fig. 1). After this, the process of sampling will still be

considered as a random gridded sampling scheme.

Figure1. One 0.5x0.5 degree grid with individual sample location on the corners and their shift to the center of a 250x250m homogeneous area

2. How will 1500 more independent samples be generated for independent validation? Answer: The already generated 1500 samples will only be used for independent

validation and now there is no need to generate another set of samples for the validation

of cropland extent map of South Asia.

3. How was the proportion of crop/No-Crop samples chosen (i.e., 67% Crop and 33% NC

sample proportion) in 1591 generated samples?

Answer: The crop proportion has been selected based on some reference source which

needs to be provided by Murali. According to Murali, South Asia has almost 75% area

under cropland which has also been maintained in sample size distribution to perform a

visual interpretation of crop/no-crop labels using high resolution imagery.

4. How will the reference labels with two possibilities be treated for crop/no-crop

validation?

Answer: Once the non-homogeneous samples labeled with two possibilities will be

moved to nearby homogeneous area, the issue of double labels will be resolved.

5. The 250m cropland extent map has already been received for South Asia. Are these

samples generated for 30m or 250m validation?

Answer: The samples have been generated for independent validation of 250m cropland

extent map that has already been shared by Murali.

6. Did you look for agro ecological zones in South Asia?

Answer: The agro ecological zones have not been used and seen yet for South Asia. But

this could be looked over by the accuracy team to perform zone wise validation in South

Asia. Figure2. 1591 gridded samples generated for South Asia Crop/No-Cop Validation

Figure3. The attribute table attached with 1591 samples