Asked and Answered Quesions from Prairie Geomatics Ltd.

1. I want to put data from my Garmin GPS into ArcView. How can I do this?
   
   The Minnesota Department of Natural Resources developed an arcview extension which allows users to upload and download Waypoints and Tracks from a Garmin GPS reciever and ArcView GIS. You can download this extension from their website: http://www.dnr.state.mn.us/mis/gis/tools/arcview/extensions.html
   
   Another ArcMap extension that can be used is called MxGPS. This program will download GPS data such as waypoints and track logs directly into ArcMap and will be stored in shapefile or geodatabase format. This program is US$64 to register.
   

2. What do I do when my unit displays a "Low Memory Battery" message?
   
   If you have a cigarette lighter adapter cable or a power data cable, plug the unit into a power source for 3 days (car, boat, etc.) to recharge the internal memory battery. If you do not have a cable, place a fresh set of AA batteries in the unit and leave the unit powered off for approximately 5 days to recharge the internal memory battery. Once the internal memory battery is recharged, the "Low Memory Battery" message should no longer be displayed. If the message persists, it will be necessary to return the GPS unit to GARMIN so the internal memory battery can be replaced. If this is the case, please send us a Technical Support email . A Return Material Authorization (RMA) will be set up and returned to you via e-mail with shipping instructions. The RMA number will ensure accurate tracking and prompt return of the unit to you. If you own an 8-channel GPS receiver unit, a marine GPS unit or chartplotter, or an aviation handheld, your unit has a non-rechargeable memory battery. You will also need to send your unit to GARMIN for replacement under our flat-rate repair program. In this case, please email GARMIN using the above link or call GARMIN Product Support at 1-800-800-1020 to arrange for an RMA number to be issued for the return of your unit. As memory technology has advanced, many GARMIN GPS units (from 1999 on) no longer require a memory battery to support user data.
   

3. What does "ephemeris" mean? 
   
   This refers to a list or table of positions of a celestial body as a function of time. The word comes from the latin word for diary. In GPS, ephemeris refers to a set of numeric parameters that can be used to determine a satellite's position. Satellite image distribution files from earth observing satellites like Landsat or ERS-1 usually have ephemeris or orbital data included in the file header; this information is ignored when using the "rubber-sheeting" method of geometric correction, but is essential when the more accurate georeferencing method called orthorectification is used. 
   

4. Who owns my yield data?
   

   You do. If you get someone else to help you create your yield maps, they can't share that information with anyone else without your permission. 

   Basically, any information that's collected on your farm 'from the ground' belongs to you... but information collected from above, like an aircraft or satellite, belongs to whoever is paying for the flight. 

   Farmers are beginning to realize how valuable their yield data is when it is combined with aerial or satellite imagery. The yield data is what's called 'ground truth' data, which can be used to calibrate a satellite image for a larger area. For example, using wheat yield data from one field, and a mid-summer satellite infrared image of several townships, and assuming similar spring seeding times, one should be able to fairly accurately estimate the yield for all similar variety wheat fields over a larger area.
   

5. How to measure field acreage?
   

   Area Calculation - using the 12XL (doc)

   Area Calculation - using the 72/76 series (doc)
   

6. How can a GPS be used for soil testing?
   

   Here's how GPS can apply to various soil testing strategies:

   Conventional Soil Testing

• agronomist, farmer and soil testing operator together select ~15 to 30 representative locations in the field
• one surface and one subsurface sample are taken at each location, the soil samples are combined and then a subsampled
• soil test locations are stored as map coordinates, so next year only the operator (not the farmer or agronomist) needs to go to the field, and the same sites are used year after year
• a map of the locations can be prepared for the farmer

Benchmark Sampling

• agronomist, farmer and soil testing operator together select ~3 to 8 locations which represent similiarly yielding areas, for example, two typical knolls, three typical midslopes and two typical lower areas in the field
• locations can be chosen based on topography, yield maps, satellite vegetation maps, and on the knowledge the farmer will have of the field
• about 6 to 15 samples are taken in a small (~25 ft) circle around the center of each location; samples are combined for the samples in the circle, then subsampled to create one composite surface and subsurface sample for each benchmark location
• a potentially more accurate fertilizer recommendation can be made using these results since higher and lower producing area numbers are not masked out as happens in conventional sampling
• in the following year, only the operator needs to go to the field
• here's what the navigation screens might look like
• various maps can be prepared for the farmer and for analysis purposes

Grid Soil Testing

• for higher value crops or for special research projects, a grid of sampling locations is chosen and samples are analyzed separately
• grid coordinates are created on computer and transferred to the GPS which used to navigate to each sampling location
• management zones for variable rate fertlilzer applications are created either on a grid basis or for polygon areas created from analysis of the grid soil test results

Zone Sampling

• satellite or aerial images from the peak crop growing period (just prior to the start of ripening) are used to compute a 'vegetation index' which measures the amount of crop biomass in the field (ideally, several years information is used)
• this vegetation index is classified into several zones which form the basis of a sampling strategy and the development of management zones for future variable rate applications
• the coordinates for the proposed sampling locations are created on the computer and then transferred to the GPS which allows the soil test operator to easily navigate to the correct locations