If you are going out into the field and have enough flexibility in your planning to factor in getting the best possible satellite coverage for your GPS data collection, the Trimble GNSS Planning Online tool is definitely worth checking out.
It needs Silverlight, so Internet Explorer is the browser to use:
While much of the information available from this service is very technical, it is good stuff to get familiar with.
For instance, DOP stands for Dilution of Precision and you will see in the chart below that there are five (5) DOPs that you can take into account at the planning stage:
GPS.gov, the official US government site about the Global Positioning System (GPS) has some easy to understand descriptions of the accuracy of GPS – and the potential differences between the transmitted signal and the received signal when using the system.
At the very least, you should have thought carefully about the accuracy and precision actually needed for your research work. This post only addresses one small section of the overall system and processes that are involved in enabling us to collect data with reliable, repeatable x,y,z coordinates attached!