Volumetric soil moisture
Volumetric surface soil moisture will be measured over 50 selected agricultural fields, by 10 field crews of 2 members each. Field crews will use Stevens POGOs to measure soil moisture at near surface depths (5.7 cm).
At each sampling location, a total of 3 readings will be taken with the 1st reading between the crop plants at the top of a ridge, the 2nd reading in the middle of a ridge and the 3rd reading at the bottom of the depression between ridges. If there are no discernible ridges, all three readings will be taken.
Two sampling methods will be adopted in order to assess:
- passive radiometer and active radar soil moisture retrieval approaches and
- field-scale variability in soil moisture to assist in scaling issues.
Sampling method 1: Flight overpass sampling
The overall goal of the flight overpass sampling is to maximize the number of fields from which representative field-scale soil moisture can be acquired for the validation of passive radiometer and active radar soil moisture retrieval approaches. It will be conducted coincident in time to flight overpasses.
There will be 16 sampling points in each field arranged as two parallel transects, one at 100 m from the road and the other at 200 m further into the field. The transects will be oriented parallel to the seed row direction to make it easier to walk between points. The end points of each transect will be at a minimum of 100 m from the field edge. Sampling points along each transect will be 75 m apart.
Sampling method 2: High-resolution soil moisture sampling (optional, if sufficient resources are available)
High-resolution ground measurements of soil moisture can provide data to evaluate variability in soil moisture within an area equivalent to RADARSAT-2 standard mode (30 m) pixel. This intensive sampling will be conducted on a limited number of fields and at the earlier part of the sampling campaign when crops are still in their early stages of growth and the variation in soil moisture will be a more significant factor affecting the microwave signatures. The high-resolution pattern will be a 50-point grid at a 15 m spacing centered on Sample Points 3 and 4 and three readings per sample point will be taken.
Temporary and permanent soil moisture sensors
In addition to the ground soil moisture measured from the abovementioned sampling methods, in-situ temporary soil moisture stations will record surface soil moisture (5.7 cm) preceding, during and after the aircraft measurement campaigns. A temporary soil moisture station will be installed on each field at either the sampling location 1 or 16 of the flight overpass sampling (sampling method 1).
Besides, AAFC permanent in situ network stations will collect soil moisture readings at discrete depths of 5, 20, 50 and 100 cm.