Interpreting Env-DATA results and FAQ

We hope that the Env-DATA System saves you many time-consuming steps in linking tracking data to environmental conditions, making it easier to test hypotheses and leaving you with more resources to design novel studies and collect high-quality data. Since we're certainly not the experts for every species, region, and environmental dataset, this is where your expertise comes in—putting the results in an interesting and realistic biological context. Here are some commonly asked questions about Env-DATA results:

How accurate are the interpolated results?

The annotated data are estimates that reflect the resolution and accuracy of the original datasets. The environmental variables available through Env-DATA come from many different products and providers. To understand the quality of these products, we recommend (1) Review the readme files that come with your results for more about the products and their QA/QC procedures, including the "Source link" and "Related websites" provided for each product you have annotated. (2) Annotate relevant QC variables when available. Links to related QC information and a list of relevant variables where available are displayed when browsing variables (click on the for a product or variable). When comparing the results of QC variables to those of other variables, consider the interpolation methods used—to compare directly it is typically best to use the same interpolation method for all relevant variables.

Consider the temporal and spatial resolution of the environmental datasets as well as the tracking data, and consider what variability and trends are biologically meaningful. For example, weather conditions from global atmospheric models do not describe local conditions and so are only an approximation of what animals actually experienced. If the location estimates for your animals have an error of 1 km, annotating 30-m elevation land use in heterogeneous environments might not be useful.

Where can I find the units, citation requirements, and other information about my results?

The readme file included with your results provides units, definitions, original resolution, links to the source and terms of use and other helpful information.

Why are my results a file with a header but no data?

This happens most commonly when annotation is requested for animals that have no associated locations. Make sure the data are correctly imported and linked to animals using deployments. Verify what data are deployed in the study by downloading the data or reference data, viewing the data on the map or comparing deployments and available data in the Deployment Manager. You can also choose to annotate data for tags rather than animals to include undeployed records.

Why do I have lots of "NaN" values in my results?

Missing data, or "NaN" values, occur when

  • The source file has periods or regions with nodata values, for example, if you request a vegetation index for a period when the animal was flying over the ocean, or sea surface temperature for a period when the animal was on land. Satellite imagery will contain more no data values in cloudier regions; likewise for locations near the poles, there may be missing data during times of year when it is nearly always dark.
  • The requested records fall outside the temporal or spatial range of the dataset: See our data products summary for the area and time covered by each product. For products that are available to the "present", there is a lag between today and when today's measurements are available as processed data files, so if you have live data feeds, the most recent few weeks or months will commonly return NaNs for these products (see an explanation from ECMWF).

Solutions: See what obvious explanations there might be for your results as described above. You can also try requesting using a different interpolation method—as described in Env-DATA Interpolation Methods (look for "missing data"), nearest neighbour or inverse distance weighted interpolation will give a valid result even if some of the neighboring data values are missing, while bilinear interpolation will not. In addition, some products include quality control variables that might indicate reasons for missing data.

How do I calculate wind speed and direction from the u and v wind?

A good resource with instructions recommended by NARR's support team is here. See the section on "geographic wind direction" and if you are using a spreadsheet program like Excel, see their warning under "two argument arctangent function" to make sure the equations work correctly.

Why do the timestamps look funny in Excel or say "00:00.0"?

If you use Excel to view your results, be aware that it can corrupt timestamps and truncate values in the annotation results. See here to learn how to avoid this problem.

How do I cite information annotated using Env-DATA?

The animal movement and environmental information you annotate are not created or owned by Env-DATA or Movebank. Always cite the original data providers when you present or publish your work. Many data providers and owners also want authors to send copies of work resulting from their products. Links to each environmental data provider's requested terms of use are in the readme file. For the tracking data, see Movebank's Citation Guidelines. To cite the use of the Env-DATA System, use

Dodge S, Bohrer G, Weinzierl R, Davidson SC, Kays R, Douglas D, Cruz S, Han J, Brandes D, Wikelski M (2013) The Environmental-Data Automated Track Annotation (Env-DATA) System: linking animal tracks with environmental data. Movement Ecology 1:3.

How can I get more help?

If you receive an email saying or request has failed, have not gotten results within a few days, or have questions about the results not addressed above, please send the access key for the request to so we can take a closer look. The access key is shown in the third paragraph of the readme file, which can also be found by going to Env-DATA > Show My Requests and clicking on Details for the request, as shown here:

Movebank study name: Golden Eagles in Alaska
Annotated Animal IDs: 12345
Requested on Tue Oct 27 20:00:33 CET 2015
Access key: 5485945721593819135
Requested by: user name

For more details about how the Env-DATA Track Annotation Service works, see Dodge et al. 2013.

The Env-DATA System

Environmental data products

Env-DATA Track Annotation Service

Interpolation methods

Interpreting results and FAQ