In this post, while not an overly complicated process, I describe the methodology that I used while performing ocean depth (bathymetry) variable work on phase 2 of the BOEM aliquot grid project. Note that, since the source data used here was also used on the phase 1 wind speed work, the process described here, with one exception (see last section describing the join process), is similar to what was carried out on phase 1. A comparison of the two extents can be found at the end of this post.

PLEASE NOTE: As all data sources/end products used/generated in this workflow are deemed public, permission to document was requested and subsequently granted.

Goal, Data Input, and Deliverables

Processing Overview

Source Raster Projection

Since the source bathymetry raster was not projected, the first step for the ocean depth work was to project the data to the NAD83 / UTM Zone 10N projected coordinate system.

Derive Zonal Statistics

With the Zonal Statistics as Table tool, descriptive statistics were derived for each aliquot cell. The stat values that were acquired were minimum, maximum, range, mean, standard deviation, and sum.

Ocean Depth Statistics To Aliquot Grid Join

The final step for the summarized ocean depth data was to join the data to the larger aliquot grid feature class.

When the join was performed, I discovered that many of the aliquots along protraction seams resulted in null values when the zonal stats tool was run. This was due to a couple reasons: The first is that there is a technical limitation in the Zonal Statistics as a Table tool where, whenever the zone boundary (in this case, aliquots) is smaller than the raster cell size that it is drawing stats from, the tool will return null for the given zone. The Esri technical document on this topic can be found here. The second issue was that, for many aliquots along the EEZ (exclusive economic zone) boundary, there was simply no bathymetry data present. This was attributed to the extents between the layers being ever so slightly different. A workaround was developed that satisfactorily resolved these issues. I will likely do a write up on that process later.

Aside from the null issue, this task was pretty straight forward. Thanks for taking the time to read! Thanks to Joel Osuna-Williams (CGST project manager) and Frank Pendleton (BOEM GIS analyst) for having me on the project.

Comparison of extents between BOEM aliquot grid phase 1 and phase 2 work