I use SonTek’s HydroSurveyor (HS) software on our Jag Ski when collecting bathymetric data. I prefer to use this instead of their RiverSurveyor Live software because of its line planning, navigation, and absolute RTK capabilities. One of the nice things about HS–when it was released–was its ability to reference aerial imagery via online map tile servers. However, this capability disappeared in early 2017 when the MapQuest tile server ceased to exist.
Not wanting to lose the ability to plan surveys with current aerial imagery in the background, I decided to figure out how to import imagery. While this capability of HS has always existed, and while it is documented in the user manual, I never had the patience to figure it out. Until I had to! Here is a step-by-step process that I followed to make this work. Note that I will reference the GIS software “QGIS” in my steps. This stands for Quantum GIS (click here). Any GIS software could be used as a substitute, but I prefer to use QGIS because it works across all computing platforms and I commonly have to swap back and forth between a Mac and a PC.
- Download NAIP imagery from USGS National Map Viewer (click here)
- The image will be a JPEG2000 (jp2). Images after 2013 are projected in WGS 1984 Web Mercator Auxiliary Sphere projection (EPSG 3857), which is exactly what you need for the HS software.
- Open your image in QGIS, define the CRS as EPSG 3857 (WGS84 Mercator)
- Save your file with a new name as a rendered GTIFF using the same CRS (EPSG 3857)
- In QGIS, go to Raster / Projections / Extract Projection. Select your file created above (tiff) and then process.
- Rename the world file with extension “tfw” instead of “wld”. (Note that the remaining steps will not work unless you complete this one. The HS software requires a world file, but you don’t get one when you download the imagery from the USGS National Map Viewer.)
- Open HydroSurveyor, select Tasks / Import Georeferenced Image, and then select your tiff file(s).
- Select WGS-84 Mercator in the following window.
- Save the tiled data with a new name.
- In HydroSurveyor, click “Add Layer” and then “Browse for File” … select your tile files.
- Note that you may need to expand your image layer using “>>” and then select “zoom to layer” in order to see your imagery.
Do you have to use imagery from the USGS National Map Viewer? No, not at all. Any georeferenced aerial imagery will work so long as you can 1) reproject it to WGS84 Mercator (EPSG 3857) and 2) extract/create/obtain the image world file. That said, another good option for imagery is TerraServer, but those images can be expensive.
Have you ever wondered what it’s like to perform a hydrographic survey on the South Alabama Jag Ski? If so, watch the short video below that captures an overview of a recent hydrographic survey of a small flood tidal shoal. While I use some different windows and information during navigation, the windows shown in this video provide a reply of representative data.
A recent expedition to Little Lagoon Pass to perform an updated bathymetric and water quality survey was thwarted by an unusually intense solar flare emission(s) (Tuesday, June 10). What, you don’t believe me? Well check {this} out.
The solar event wreaked havoc on the land-based GNSS system, limiting us to collecting less than 100 elevation points on the flood shoal. We were able to survey the flood shoal and channel using the Jag Ski system, as well as perform a water quality assessment of the lagoon.
We will return to the site in the next two weeks to conduct a complete field survey of the ebb shoal and beach profiles, as well as touch up what we missed on our earlier visit. At the end of the day, the sun left us with little more than minor burns and an ill-functioning GNSS system.
The South Alabama Jag Ski was recently used to map bathymetry and velocity at selected locations in northern Mobile Bay as part of a hydrodynamic model (ADCIRC) study of the area. Bathymetric data were collected in order to update the ADCIRC model mesh and underway velocity profiling was performed for eventual model-data comparison of velocity/discharge and water levels. Areas sampled include:
- I-10 Cut west of Choccolatta Bay
- Existing box culverts east of the I-10 / Causeway interchange
- Pass Picada
- Apalachee River
- Sardine Pass
- Duck Skiff Pass / Justins Bay
- Blakeley River
Our two-year monitoring project with ALDOT got off to a great start on April 12/13 at Little Lagoon in Gulf Shores, AL. The purpose of the project is to monitor and evaluate impacts of proposed modifications to Lagoon Pass on the adjacent beaches. The HWY 182 bridge is being replaced, the channel widened, and the north/south pass jetties extended into the Gulf. Monitoring includes hydrographic surveys of cross-shore beach profiles (i.e. transects), the flood and ebb tidal shoal volumes, and channel depths. Traditional land-based surveys of the dry beach, as well as some areas of the flood shoal too shallow to survey by boat, are also performed along the same transects as those performed by the South Alabama Jag Ski (photo at right) on the water.
Despite some technical difficulties with our GPS equipment, likely due to the passage of a severe storm days before, we were able to complete most of our survey plan. Our survey team, consisting of Drs. Scott Douglass and Bret Webb, Richard Allen, Drew Harrison, Kari Servold, and Tim Wicker, collected over 24,000 elevation measurements while spending over 20 hours in the field over the two-day period in early April. A failed calibration of some instrumentation prevented a water quality survey of the lagoon during our trip, but the Jag Ski will be headed back to the lagoon to complete that mission in the coming weeks. A special thanks to Clay McCoy for helping us in the field on Saturday morning.
