Frequently Asked Questions
What are "Mascons"?
You can imagine mascons, or "mass concentrations", as discrete cells located across the Earth's surface, each with their own small gravity signal. When viewed as a whole, all the mascons sum up to Earth's full gravity field. Viewed individually, each mascon cell represents the gravity signal of a particular area. Because these mascons are in discrete locations across the globe, regional studies of water storage changes are simplified. In this tool, each mascon shows the local changes in gravity in the cell due primarily to water moving into and out of each cell.
What are "Water Equivalent Height" units?
"Water Equivalent Height" is a way of representing changes in the gravity field in hydrological units. A +1 cm change in Water Equivalent Height in a certain mascon is like saying that mass has been added to the cell equal to water spread out over the entire mascon 1 cm deep. So, with some exceptions, positive changes correspond to the mascon becoming wetter, and negative changes correspond to the mascon becoming dryer.
What happens when you "deseason" the data?
The tool uses least squares to estimate the trend in the data before plotting. As part of the estimation step, annual and semi-annual signals are also estimated. When you choose the "deseason" option, these signals are removed from the data and all other variations remain.
What does the Coastline Resolution Improvement (CRI) filter do?
JPL uses a Coastline Resolution Improvement (CRI) filter to separate land signals from ocean signals in those mascons that are along the coast. As a result, land areas and ocean areas within the same mascon will return different signals when this filter is applied.
Is the data on this site different from the source JPL RL06M v02 data?
We restore the mean atmospheric mass over the oceans in order to convert the data over the oceans from Ocean Bottom Pressure (as provided in the solution) to Ocean Mass using GRACE Technical Note 12 (see GRACE Documentation for more details. For data in units of Gigatons, the JPL-provided water equivalent height units have been converted using calculated mascon areas based on the 0.5 degree grid cells distributed by JPL.
Why doesn't the GSFC solution include a coastline filter?
GSFC and JPL use two different solution methods and least squares constraint strategies to develop their respective mascon solutions. The GSFC solution uses many more and much smaller mascons (approximately nine times as many mascons) to represent mass changes across the earth, and therefore those mascons naturally afford better adherence to coastlines than JPL's.
What are the Regions and Basins shown?
GSFC distributed their solution with Region and Basin metadata attached to each mascon. On this site, that metadata has been used to calculate the additional region and basin information displayed. This is not post-processing done by us, but rather a full visualization of the data provided by GSFC.
The website does not appear to be working for me. All I see is a gray box where the map should be!
The site uses a mapping tool called Mapbox GL, which uses WebGL for fast map rendering. It is very likely your browser either does not support WebGL, or it is disabled. For example, Chromium and Chrome for Linux users will likely need to enable WebGL in their browser (try here for potential help). You may need to Google how to enable WebGL in your browser, or try another browser: Chrome, Firefox, and Safari all appear to work.
I think I found a bug. Who should I contact about it?
Thanks for the help. We believe that the site is fully functional, but since it is new and features are being added periodically, it's possible something might break. Please go to the Contact page and get in touch with Mike Croteau. Please share any information that you think might help track down the bug, including your browser.