GPS/Data Collection Field Kit

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Here's a homemade field data collection kit. Acquiring every part shown here is not essential for improving field data collection practices, but each piece adds functionality as explained below.

1. A Garmin GPS76 recreational grade GPS unit ($200 to $400). These units accept cables for (A) an external antenna and (B) a data/power port.

2. A Garmin low-profile external antenna ($62) with a magnetic mount attached to a wooden pole gets clear satellite signals under most conditions. The external antenna is a must if you need your hands free for other field tasks. A rubber band around the GPS unit keeps the cables connected when the unit is stowed away in a pocket. Once connected to an iPAQ PDA (3), you don't need to handle the GPS unit at all.

2005 Update: If you want to collect GPS coordinates along with other data on a PDA or tablet PC, get a Bluetooth GPS receiver. It will eliminate half the cables shown here.

Be aware of a serious drawback with using a PDA or tablet PC for collecting GPS data cannot allow the data recorder to go into standby mode. Standby is SOP if you haven't touched the screen for a few minutes, as when you are walking between plots. Standby mode causes a break in the GPS-data collector "handshake". When the handshake is broken, you'll need to re-initialize the whole process. That can be quite time consuming.

If you are using a Bluetooth GPS, also be aware that separating the GPS receiver and data collector by more than about ten feet (like when you lay down the tablet PC to go measure a tree) will break the handshake.

After a number of field trials, my personal preference for forestry reconnaissance is to operate the GPS and PDA separately. Waypoints can be easily correlated to data points, and the tables can be joined back in the office.

A setup like the one described on this page would probably be most practical in a plane, car or ATV where you can supply continuous power.


3. An iPAQ PDA (about $400) running Vito SmartMap ($30) for navigation and FS Tally Meter ($0) for data collection. TinyStocks Navio ($20) and Delorme XMap Handheld Pro ($50) are a couple other GPS map/navigation programs that I like.

4. An Otterbox® Armor 3600 rugged case ($100) and data cable port ($40) protect the iPAQ from water, dust and bumps on rocks. One of the advantages of the case is that it prevents the PDA serial/power connector (which has light-duty spring clasps that break away with the least lateral force) from being detached.

The Otterbox is a well-engineered work of art. With the back half removed, you can see the Velcro straps that hold the PDA in place. There's also a foam pad, not shown, to  insert behind the PDA. The blue SD card can be removed for data transfer without un-strapping the PDA. The end cap has secure rubber gaskets that have a firm grip on the cable so it can't be pulled out. The standard Armor 3600 is deep enough to accommodate an iPAQ battery-CF expansion pack.

5. A RoadPro 12-volt lead-acid rechargeable battery ($30). The battery includes an AC adapter for recharging. The battery powers both the PDA and GPS unit through the cable box (6). I've left both the PDA and GPS unit run for eight hours with no lack of power. The 12-volt battery constantly recharges the PDA battery. (Take care to keep the battery fuse cap screwed on tightly or the power supply will flicker, which could cause the GPS unit to turn off.) The battery weighs about 2.5 pounds and fits in the back pocket of the field vest.

6. The data/power cable ($60) is from SupplyNet. It connects the GPS unit to the PDA and has a cigarette-lighter adapter that plugs into the 12-volt battery, providing power to both the GPS and PDA. SupplyNet makes the cables for a wide variety of GPS/PDA models.


7. A field vest holds the GPS pole, GPS unit and 12-volt battery. The wooden pole is attached to the inside back pouch of the vest with three screws through the fabric into the wood. The metal platform for the magnetic-mount GPS antenna is nothing but an empty Altoids mint tin! The rubberized magnetic base on the antenna is strong enough to stay in place even through a brush tangle. (A custom backpack with a telescopic GPS pole would be nicer, but more expensive.)

The cables between the antenna, GPS unit, battery and PDA are somewhat restraining and take getting used to. Another option would be to use a wireless, pole-mounted GPS unit. They are becoming more affordable. The Otterbox also has an optional deep back to accommodate a battery expansion pack for the iPAQ PDA.

Do you need everything listed above? Not necessarily. In terms of practical value, I'd assign these priorities:

1. A recreational grade GPS unit. It's invaluable as a navigation tool and for recording fairly accurate locations of plot data.

2. An external antenna for a GPS unit (if yours accepts one). Not needing to constantly orient the GPS receiver for optimal signal reception frees your hands for other tasks. You can put the GPS receiver in a pocket and just pull it out to record waypoints or to reference a position. In the winter, you could put the GPS receiver inside your coat to maintain battery power. (Cold weather significantly decreases the life of NiMH and alkaline batteries. Lithium AA batteries, which operate to -40°F, are another option for cold weather use and extended battery life.)

3. A Pocket PC. A digital data recorder can save significant time whether you use a simple, free data program like FS Tally Meter or a sophisticated program such as 2Dog or TCruise. A clipboard and paper are much cheaper, however, and easier to operate in extreme weather.

4. A ruggedized PDA case. You can use your PDA inside a Zip-Lock bag to keep it dry, but an Otterbox or similar rugged case with a strap protects the PDA from impacts and makes it easier handle. If you intend to connect the PDA to an external battery or to a GPS receiver, a rugged case can also help prevent cables from becoming disconnected.

5. An external power supply. GPS receivers and data recorders require dependable batteries. The batteries contained in the units might get you through the day (or you can carry spare batteries). Having an external battery with more than enough power for a full day is, however, an advantage. The trade offs are the extra weight and cables.

6. Cables to connect the GPS receiver, PDA and possibly an external power source. A GPS and PDA work fine independently, but it's an added convenience to view the GPS controls on the PDA and to automatically record GPS coordinates with plot data. The more cables involved, however, the more difficult it is to maneuver in the woods. Connecting a GPS to a PDA may also make it undesirable to power-off the PDA between plots, increasing the power demands for the PDA.

7. A GPS-enabled mapping program for the PDA. Viewing locations on a GPS receiver screen is adequate for basic navigation, but seeing your real-time location displayed on an aerial photo, topo map or other specialized map can be a fabulous advantage.

If you have $5,000 or so, you could also buy a dedicated field data recorder from companies such as Trimble or Leica that combine all of the above features in one unit. Some dedicated field data recorders include additional features such as a screen warmer and differential GPS corrections.

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