Using Landsat and flow lines and sinks from LiDAR-based elevation data to compare yield and drainage patterns for a field of interest to others under a similar rain regime
Related page: LiDAR-Based Elevation, Drainage & Topography Layers
It was found in Illinois that 2-mile rain gauge spacing explained 90 percent of May through September storm variance (Huff, 1979; pdf). In other words, it is necessary to have rain gauges spaced at two-miles to account for 90 percent of rain differences because rain amounts are different enough 2 miles away. Steps to compare a soybean field to others within a 1.5 miles radius using Landsat and LiDAR-based elevation data are shown below, but this can be applied to corn or other crops.
Points of this analysis are to determine how a field of interest operates under challenging rain conditions compared to neighboring fields that are likely to have similar rain conditions as well as how well a field operates. The imagery is near infrared for a time when values correlate to yield well for soybean fields.
1) In the image below, orange point is center of field of interest and orange line encompasses 1.5 mile radius around point. Soybeans are lighter shades, corn is medium, and harvested fields are darker.
2) LiDAR-based elevation; data is resampled from a 2.5 foot resolution to a 5.0 foot resolution (original data was based on 2 meter average post spacing for state of Ohio [OGRIP, 2012).
3) Flow accumulation lines with appropriate coarseness so they show lower ground soil areas at field scale.
4) Soybean fields are outlined in green. You can now zoom in to see how different fields perform under same heavy rain regime; comparison are shown below between heavy and more ideal conditions for same field.
5) Comparisons are shown below for fields corresponding to heavy rain (2006) and less heavy rain (2010) conditions during earlier vegetative stages. The image on the left represent the 2006 season where there was heavy June precipitation (6.52 inches measured at county rain gauge in June) after soybeans were planted (planting was done on time). The image on right represents a season (2010) with plenty of June rain but still significantly less. Lighter shades of Landsat pixels correlate to better crop condition and higher yield. The green lines outline the valid Landsat pixels (pixels that only represent the field; they are not averaging in outside areas) that should be assessed. Flow accumulation lines are in darker blue and sinks (areas that pond) are in lighter blue. The comparisons for the next three fields show that overall the fields have higher yields in lower ground soil areas in the season with less rain; the last two images show fields that did not show problems in lower ground soil areas for the same wet 2006 season.
Drainage Analysis for Field of interest
(season that was rainier in earlier vegetative stages is on left)
Field showed signs of drainage problems on western side of field in rainier season.
Fields within 1.5 mile distance of field of interest
(season that was rainier in earlier vegetative stages is on left)
Fields showed signs of drainage problems in rainier season.
Fields within 1.5 mile distance of field of interest
(both fields are from season that was rainier in earlier vegetative stages)
Fields showed fewer signs of drainage problems than previous fields.
Reference
OGRIP. 2012. Ohio Geographically Referenced Information Program. Cited at: http://ogrip.oit.ohio.gov/