GOES Imager Projection (ABI Fixed Grid)
Information on this page is adapted from the GOES-R Series Product Definition and User’s Guide (PUG), Volume 5: Level 2+ Products, Section 4.2.
What is the GOES Imager Projection?
The GOES Imager Projection, also called the ABI Fixed Grid, is the projection information included in all ABI Level 1b radiance data files and most ABI Level 2 derived product data files. It is a map projection based on the geostationary viewing perspective of the GOES-East or GOES-West satellite.
The GOES Imager Projection information is used instead of latitude and longitude, to save ABI data file space. As a result, latitude and longitude are not included as separate variables in most ABI data files, including the Level 2 files we use in our training sessions (e.g., ADP, AOD, FDC).
What does this mean for you as an end user? It is possible to work with ABI data using the GOES Imager Projection directly; an example of GOES-16 ABI CONUS sector band 2 radiance (L1b) data visualized using the GOES Imager Projection is shown below. Note the distinctive “curved” view of the Earth from the geostationary satellite projection (click image to open full size version).
Calculating Latitude and Longitude from the GOES Imager Projection
If you want to work with ABI Level 2 files using latitude and longitude to plot the data variables (e.g., ADP, AOD, FDC), then it is necessary to calculate latitude and longitude from the GOES Imager Projection information.
The figure below shows the coordinate frames for the latitude/longitude calculations. For a given point P on the Earth with ABI fixed grid coordinates (y, x), the latitude (φ) and longitude (λ) can be calculated using a series of equations, provided in the GOES-R PUG.
Coordinate Frames for GOES Imager Projection (ABI Fixed Grid) Navigation
(image courtesy of GOES-R PUG; click image to open it in a separate tab)
All of the information needed to calculate latitude and longitude are provided in the ABI data file:
- x variable (fixed grid E/W scanning angle in radians)
- y variable (fixed grid N/S elevation angle in radians)
- req (semi-major axis)
- rpol (semi-minor axis)
- H (perspective point height + semi-major axis)
- λ0 (longitude of projection origin)
Don’t worry! We did the math for you. We provide a Python function that can be used to calculate latitude and longitude from the GOES Imager Projection information in any ABI Level 2 data file.
Download Files Containing Latitude and Longitude for 2km Resolution Full Disk & CONUS Sectors
If you are working with ABI Level 2 files for the full disk or CONUS sectors, it can be easier to read in the latitude and longitude arrays for the ABI fixed grid from external netCDF4 (.nc) files, instead of calculating the latitude and longitude arrays on the fly from the GOES Imager Projection information in the Level 2 file.
Below are .zip files that contain the latitude and longitude .nc files for the current GOES-East and GOES-West full disk and CONUS sectors at 2km spatial resolution, which is the resolution for ADP, AOD, and FDC data files. Download these files & extract and save the contents, and then you can simply open the appropriate file and read in the latitude and longitude arrays.
Full Disk & CONUS sector (2km resolution) ABI fixed grid latitude and longitude .nc files:
- Download GOES-East (GOES-16, 75.2 °W) 2km resolution Full Disk sector lat/lon file (61.5 MB)
- Download GOES-East (GOES-16, 75.2 °W) 2km resolution CONUS sector lat/lon file (9 MB)
- Download GOES-West (GOES-18, 137.0 °W) 2km resolution Full Disk sector lat/lon file (59 MB)
- Download GOES-West (GOES-18, 137.0 °W) 2km resolution CONUS sector lat/lon file (8.5 MB)
If you are working with mesoscale sector files, then you will have to use the provided Python function to calculate the latitude and longitude arrays on the fly from the GOES Imager Projection information in the ABI Level 2 file. This is because unlike the full disk & CONUS sectors (whose locations do not vary), the locations of the Mesoscale sectors change depending on current hazards.