Digital LUC survey

An experimental digital LUC survey was carried out in Northland between 2015 and 2017. The work was funded by Ministry for Primary Industries (MPI) under their Sustainable Land Management and Climate Change (SLMACC) fund.

Comparison of traditional LUC unit mapping (on left) and digital LUC unit mapping (on right) for one of the study areas.

The objective was to determine whether detailed property-scale LUC surveys could be carried out using a combination of LiDAR imagery, digital soil mapping and other techniques over 100 km2 and to compare the resulting LUC maps with traditionally prepared property-scale maps executed by a well established LUC consultant working under "business-as-usual" conditions.

A detailed report of the findings of this research project can be found at https://www.mpi.govt.nz/dmsdocument/30615 

  • Rock type was derived from a modified regional-scale map because resolution of available radiometric data was too coarse for property-scale mapping.
  • A raster slope map was derived from the LiDAR survey to a very high accuracy and precision compared to visual interpretation.
  • Similarly, a raster digital soil map was prepared based on extensive field survey (500 auger observations) and geostatistical analysis of soil classes with raster covariate layers including the rock type, slope and other terrain-based variables.
  • Erosion was assessed using a targeted field inventory and interpretation of very high resolution aerial imagery captured during the LiDAR survey.
  • Vegetation was taken from the Land Cover Database (LCDB v5.0).

A segmentation process (grouping similar raster cells) was used to vectorize both the slope and soil maps, and these were combined to generate a set of LUC polygons. The polygons were then populated with inventory attributes based on all five of the underlying inventory layers created for the project.

A property-scale extended legend was developed from the original Northland Regional Extended Legend, and map units assigned to an LUC unit based on their inventory factors. This used a rules-based approach similar to the keys to recognising LUC units found in the Regional Report series for the NZLRI.

In many respects the process mirrored traditional LUC mapping, but used digital rather than manual techniques to generate LUC polygons and then codifying the rules-base behind the extended legend to assign LUCs. It is important to note that was not a mere desktop exercise and still involved significant field effort.

An example of the final result and comparison to traditional mapping is shown in the image above. For more detail refer to the full report.