4.02.2012

Off-the-fieldnotes: On fieldworks using Handheld receivers

Last week was one tedious week, part of my primary data gathering is to map all the storm drains within my study area for my thesis. That was about 371 hectare area of land with a mix of residential, commercial and industrial land uses. I have used 2 types of Garmin Handheld receivers for this part, the Garmin Oregon 550 and the Garmin 76CSx for this storm drain inventory and mapping field work.


I would say that both are pretty good in terms of accuracy for a handheld receivers with a purpose of mapping  features just for reconnaissance or coarse accuracy requirements. Here are my rants/raves two cents for fieldworks utilizing handheld GPS receivers i.e. GARMIN GPSmap 76CSx and Oregon 550.
  • Do understand the primary purpose or objective of your data gathering and use the right tool for such purpose.-  You can't use a handheld GPS receiver to plot the corners of your lot and use it as an evidence for a land grabbing case. Have a clear understanding of the capabilities of the GPS device that you are using. The handheld GPS are of  the lower accuracy type with an accuracy buffer of 10-30m so if you are, for example, trying to map all the trees within the neighborhood or for my purpose map all the storm drains to locate inlet locations for my flood simulation, the accuracy of a handheld receiver is already sufficient. 
  • Use Alkaline batteries if rechargeable NiMH batteries are not available. - As you may know, GPS devices are power hogs. This is the major reason why your iPhone drains faster than usual when your location services that utilizes GPS are turned ON. So for your purpose of mapping, if you've got one large area to cover, better make sure you have lots of spare batteries at hand. Based on my experience, the Alkaline batteries (Energizer) lasted for 8 straight hours for the Garmin GPSmap 76Csx while it only lasted for almost 4 hours for Oregon 550. The longer performance of the 76CSx would be understandable since it doesn't have a camera that uses up much power unlike that of the Oregon 550. On my first day, I have used Eveready but to my dismay, it only lasted for 2 straight hours of mapping so I have to readily change batteries which is very much of a hassle. NiMH are also good choices for it lasts about 5 hours for the Oregon 550 but you still have to bring spares for longer mapping works.
  • Make sure to immediately save all your data gathered when you come back at the office. - This is my HARDLY LEARNED lesson . I have tried Oregon 550 first and since it has a support for memoru expansion, I didn't have worries for memory shortage. To  my dismay, the GARMIN 76CSx can only save up to 1000 waypoints. I am an hour before my last 3 kilometer stretch for the week-long fieldwork and I already ran out of waypoint memory. Too bad, I can't delete the previously gathered points :(. So unless you have a laptop onfield to readily save your data, better make sure to have it backed-up and deleted on the GPS receiver memory to allot more space for your recent observation points. For me, I have installed the MapSource program to receive and upload data from my computer to the GPS device. It has an option to save your data in GARMIN database, GPX (GPS exchange format), and TXT format for further processing :)
  • Plan your route ahead. There is indeed no better substitute to a carefully planned fieldwork. It would definitely save you much of your resources- time, money and effort. Just as there may be slight deviations from the original plan, plannning ahead is still the best way to commence every field data gathering exercise.
  • Lastly and Again know your device before going on field! - Part of the carefully planned fieldwork is a thorough knowledge on operating the device that you are going to use. Familiarity is the key. For user-friendliness, I like the Oregon 550 more because it's already in touch-screen interface as compared to the 76CSx which is still operated by button. I never really had a hard time getting used to Oregon 550 but the 76CSx is a whole new different story. I don't know if it's just me and my stupid nature that took me an ample 2 hours to figure out how to mark waypoints using the GARMIN 76CSx. So for the record, HOW TO MARK A WAYPOINT USING GARMIN 76CSx, Just long press the ENTER button and there you have it! (^_^)  The deleting of waypoints and tracks are also harder ones or I guess less intuitively designed ones. You can figure it out by pressing the menus over and over again. So yeah, FAMILIARITY IS THE KEY! So don't hesitate to explore your devices first or you'll have the entire day out on field exploring on how to use it...
  • Oh no, beforeI forget...In case you ran out of space for waypoints in your Handheld GPS and you still got a phone powered by GPS (that's not yet on a low battery!) ... you may opt to use it for mapping purposes too! I seemed to have been really frustrated when I ran out of waypoint memory and forgot to use my HTC Mozart which is also capable of geotagging photos. So yeah, for my next field mapping work, I would be very much reminded of using my usual buddy for my location-based needs:) Since our modern smartphones nowadays are already GPS powered, it works pretty much like our handheld receivers with Assisted GPS (AGPS) capability. This AGPS utilizes the location of the nearest cellsite to easily "assist" fix your position. Very nice indeed. This is a photo taken from my fieldwork for which I have turned on the location option everytime I take photos. When I tried geotagging it in Picasa, it appeared to be about 10m off the original location as specified by the Handheld GPS which is fairly ok for mapping purposes. 


Just are there are no fast rules, I hope this helps and I'm sure I'm getting more of these hardly-learned lessons that I will gladly share and chronicle here in my blog in the days to come...just so until I'm done with my data gathering part of my thesis  #fieldworkIsMoreFun (^_^)

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