Feature

Mobile Computing Goes to the High Seas

by Kyle Bohnenstiehl

The Problem

Navigation on the ocean for recreational boaters is often problematic in remote areas because existing charts are difficult to obtain, very costly, out of date, or not of a scale suitable for recreational needs. Recently, we planned a trip to the Sea of Cortez between mainland Mexico and Baja California to explore a series of five islands. We wanted to see if a small inflatable boat with an outboard motor could be easily transported into the country, equipped with enough food and fuel, and piloted on the ocean safely to have an enjoyable trip.

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 Base Map

Satellite Imagery for Navigation

The lack of good charts for this purpose was noted right away. We needed to be able to see shallow areas where the propeller might get caught on the bottom, identify possible beaches to camp on, and most importantly identify areas that might be worth visiting for their hiking and scenic qualities. LANDSAT data at 28.5 meter resolution that is part of the NASA global dataset of orthorectified imagery was downloaded and subset to the area we were visiting. Local villages, lighthouses, and other cultural features were plotted on the basemaps. We then digitized a proposed route taking into account the 200 mile range of our boat. We were able to design a schedule that worked for our limited time away from work, while seeing some of the highlights of the region.

Most importantly, we could identify coves and bays that might provide refuge in case a storm were to come in. We could also pick out potential campsites that had nice protected, sandy beaches. These were uploaded into the GPS as waypoints. We also knew that strong winds were sometimes present during the day and we wanted to be able to travel at night, relying solely on GPS for navigation from one camp to another.

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 Puerta San Francisquito

We had both hardcopy laminated maps, GPS waypoints, and ArcPad running on a Compaq IPAQ. It was nice to have all three sources of data for navigation. When we were underway on the ocean, the GPS and the laminated maps were the only way to view our course. At camp, it was nice to have the IPAQ to look at the imagery at full resolution and digitize the day''s actual route from the GPS data we collected while underway. The IPAQ also let us record audio sounds and make trip notes in the word processor.

Mobile Computing Goes to the High Seas Continued…

 IPAQ

Other Technology

For safety''s sake, we had an Iridium satellite telephone that let us get weather forecasts, stay in touch with friends and family, and most importantly call the Mexican Marine rescue service in Kino Bay, Sonora should any problems arise. The ability to receive email for free using Iridium''s SMS service was a nice plus.

 Iridium

Our boat was a Nissan Marine 14ft inflatable raft with a rigid floor and inflatable keel. The maximum carrying capacity was 1400 pounds. We had a Honda Marine 30 HP four stroke outboard and a backup Honda Marine 2HP four stroke outboard. Both engines performed flawlessly, despite being swamped by 5 foot waves on several occasions. The fuel economy was impressive on the larger motor, usually averaging around 10 mpg. The entire boat, motor, and assorted gear fit into the back of a mid-size pickup truck and could be covered with a tarp for security.

 Honda Marine 30 HP Outboard

The Results

The satellite imagery was very useful. We were able to identify excellent campsites and navigate directly to them. The imagery also provided useful bathymetry information when crossing shallow sandy areas. Most important though was the ability to navigate at night. During the day strong winds made progress wet and unpleasant -- so navigating with full confidence that we would be able to land on a good beach in what is otherwise a rocky, forbidding coastline -- was a tremendous asset. Overall, it was an excellent trip that I entered into with no small amount of fear given the treacherous currents, great distances in a small boat, and lack of good maps of the area. If you would like more information on this remote wilderness so close to the United States, email me at kyle@nagis.com.

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 Final route

Kyle Bohnenstiehl has been involved in remote sensing, GPS and GIS for over 10 years and is currently a remote sensing scientist with the Department of Interior. His work has taken him throughout the Andes of South America and the desert Southwest where he has worked with tribes, NGO''s, government and private sector groups to create innovative solutions using the latest geotechnology. He can be reached at Kyle@nagis.com