The HydroLite-TM from Seafloor Systems, Inc. is an integrated hydrographic surveying system that combines automated survey data collection in a compact and portable package. It combines water-depth data from a shallow-water echo sounder with horizontal positions from a mapping-grade GPS receiver. The end result is fast, accurate, hydrographic data collected easily and safely.

How It Works

The HydroLite-TM gets water-depth data from an Ohmex SonarMite BT shallow-water echo sounder (the BT means the SonarMite is equipped with Bluetooth connectivity). They use the term “shallow water” to describe the depth range of 0.3 meters to 75 meters, although I have a hard time thinking that 225 feet of water is shallow. Unlike fish-finder-type devices that use wide beams and average-water-depth data, the SonarMite uses a narrow beam to provide independent “pings” that define the water bottom in greater detail. The transducer element, designed for Ohmex survey-grade products, overcomes many error sources associated with older analog transducers by applying data processing algorithms and filtering. This also allows a quality value to be shown with every depth measurement and displayed in real time on the data collector screen.

Mapping-grade horizontal positions are provided by the Trimble GeoXT handheld device, which also serves as the data collector running Windows Mobile. The GeoXT is loaded with features. Bluetooth and Wi-Fi make connectivity a breeze, and the SD card slot makes data storage and transfer secure and easy. The internal antenna works well and means less setup with fewer connections. Just make sure you mount it high enough to keep your body from interfering with satellite reception.

Before I get started talking about using the HydroLite, I want to compliment SeaFloor Systems on providing a great Pelican Case. When you make an investment in survey equipment, you want to know it will be well protected and perform well for many years. With five safety latches, custom-shaped padding, and retractable handle and wheels, the HydroLite is well protected and easy to transport.

I chose to test drive the Hydrolite on a nearby creek. It uses a transom-type mount to easily attach to your boat just like a trolling motor. I used an aluminum jon boat, but you could just as easily use other watercraft. For example, I saw a picture on the internet of a creative kayak setup. A board was strapped across the top, and then a trolling motor was on one side and the HydroLite on the other. You could also use a jet ski, bass boat, or whatever makes the most sense for your project.

The HydroLite feels like a typical piece of survey equipment mounted on a prism pole. The only cable connects the transducer to the echo sounder. The echo sounder connects to the GeoXT by Bluetooth. The GeoXT has an internal antenna and receives real-time beacon corrections. Just make sure you place the transducer in the water before turning it on. The transducer will send data only when it’s submerged.


Setup was quick and easy. The SonarMite powers on when you connect the transducer cable. After powering up the GeoXT, I used GPS controller to see that I was tracking satellites and outputting positions. I then launched SMmobile on the GeoXT and set the ports for the GPS and the SonarMite data. I assigned a file name and started surveying.

Before I began collecting profiles, I wanted to do a static barcheck. The speed of sound through water can vary depending on the water’s temperature, salinity, and turbidity. If unaccounted for, this can be your largest source of error. I found a spot about six-feet deep that had a nice, hard bottom and measured from the transducer. When I compared this to the HydroLite’s reported reading, I was within less than a tenth of a foot. Considering my maximum depth is 9.3 feet, I felt pretty good about the check.

As I began working my way back and forth down the creek, the main screen shows a “bread crumb”-type trail of my path in the top window. The bottom window can be set to show the depth profile or current depth and data quality. (I prefer the depth and data quality view.) You can adjust the data quality filter to suit the environment you are working in. Dropping the filter to 80 allows more data to be used, while raising the filter to 120 may yield not as many measurements but ensures better measurements. As I watched the bottom window on the GeoXT, my measurements had a quality rating between 100 and 110. Good data.

It really didn’t seem like a work day at all. I was having fun cruising along the water. A nice breeze was blowing, the sun was shining, and the HydroLite was doing all the work for me.

The section of creek I was working in was small enough to run profiles without navigating them. If you are working in a large area, you can create waypoints in the GeoXT and navigate to them. This insures that adequate coverage helps get the job done more efficiently. After about an hour on the water I had covered my project area and was ready to head back to the office.

Data can be transferred from the GeoXT to your PC through the charging cradle and USB port or Bluetooth connection. I placed an SD card in the slot and copied the files to it, then plugged it in my PC. Importing files to the SonarVista software provided an instant display of my data. Editing tools are built into SonarVista, or you can export the data in several different formats. One export option is to a kml file that can be opened in Google Earth to check the project coverage or for a quick and easy photo exhibit.

The combination of mapping-grade positions with water depths works great in static-water situations. It works well in tidal influenced areas, too, but you need to be near a tide gauge or keep up with water elevation changes and apply the adjustments to your data.

Another option is to use a survey-grade GPS receiver. The HydroLite-TM is compatible with Trimble Survey Controller, Leica, and GPS receivers. If you have survey-grade elevations, you would not be affected by water-level changes, and the required data adjustments would become very simple.

The HydroLite-TM provides a streamlined tool for completing hydrographic surveys. Its integrated design and portability can help get the job done better, faster, and easier.

About the Author

  • J. Craig Brewer, PLS
    J. Craig Brewer, PLS
    J. Craig Brewer, PLS is owner of Brewer Land Surveying in Savannah, Georgia. He has over 15 years of experience and is a licensed professional surveyor in Georgia and South Carolina.

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