GOES-R Total Precipitable Water
Frequently Asked Questions about the GOES-R Total Precipitable Water Product
1) What is this product?
The GOES-R Total Precipitable Water product produces TPW values (from the surface up to 300mb) in millimeters (which is converted to feet locally in AWIPS) for all pixels containing no clouds. The TPW product's horizontal resolution is 10km. The GOES-R TPW product is created both day and night. It is accurate to within 1 mm (0.04 inches), and has a range of 0 to 100 mm (0 to 3.9 inches). The GOES-R TPW product is not produced beyond 67 degrees local zenith angle.1
This product is useful when trying to assess the location of enhanced moisture and/or boundaries (such as fronts or the dry line).
2) How often do I receive this data?
The cadence of the GOES-R Total Precipitable Water product is dependent upon which image from the satellite one is looking at. For Full Disk imagery, an image is produced every 60 minutes. For CONUS imagery, an image is produced every 30 minutes. For a Mesoscale scan, an image is produced every 5 minutes.
3) How do I display this product in AWIPS-II?
To display this product in AWIPS-II, go to the "GOES-R" tab of the CAVE menu, then select "Derived Products." From there, select the region of interest (GOES-E, GOES-W, or GOES Test and Full Disk, CONUS, and Mesoscale). Then, select the Total Precipitable product.
Alternately, use the AWIPS Product Browser. Select "Sat", then either "GOES-16" or "GOES-17". From there, choose "Full Disk", "CONUS", or "Meso", then select "TPW."
4) How do I interpret the color maps associated with this product?
Darker colors imply areas of high TPW while lighter colors imply areas of lower TPW?
5) What other imagery/products might I use in conjunction with this product?
The GOES-R TPW product can be used in conjunction with the Blended TPW product to see comparisons between the two datasets. Wind barbs from either the GOES satellite or weather models can also be overlayed to identify areas of moisture advection.
6) How is this product created?
The GOES-R Total Precipitable Water product is only calculated on pixels that are determined to be either "clear" or "probably clear" by the GOES-R Cloud Mask algorithm. It utilizes GOES-R bands 6.2 um, 7.0 um, 7.4 um, 8.5 um, 9.6 um, 10.33 um, 11.2 um, 12.3 um, and 13.3 um channels.. The GOES-R TPW product relies on the infrared observations to avoid discontinuities assosciated with the transition from day to night. The algorithm performance is sensitive to imagery artifacts or instrument noise.1
The ancillary data used to calculate the total precipitable water include1:
- Surface pressure from 6–18 hour forecast from NWP model.
- Surface pressure level index from 6–18 hour forecast from NWP model.
- Near surface wind speed vectors (zonal and meridional) from 6–18 hour
forecast from NWP model.
- Surface skin temperature from 6–18 hour forecast from NWP model.
- Temperature profile from 6–18 hour forecast from NWP model.
- Moisture profile from 6–18 hour forecast from NWP model.
- Forecast error covariance matrix from comparisons between forecast and radiosondes. Assume there is no correlation between temperature and moisture in the error covariance matrix.
- Land Mask
- Surface Elevation
- Temperature profile
- Water vapor profile
- IR SEs for ABI bands from UW-Madison baseline fit database. A global database of monthly IR land SE derived from the MODIS operational land surface emissivity product (MOD11). Emissivity is available globally at ten wavelengths (3.6, 4.3, 5.0, 5.8, 7.6, 8.3, 9.3, 10.8, 12.1, and 14.3 µm) with 0.05 degree spatial resolution. Monthly SEs have been integrated into the ABI spectral response functions to match the ABI bands.
- LUT for ABI IR SEs over ocean as a function of LZA and wind speed above ocean surface. (http://ams.confex.com/ams/pdfpapers/104810.pdf).
- Regression coefficient file. This coefficient file contains 81 regression coefficient datasets. Each coefficient dataset corresponds to one LZA ranging from 0 to 80 degrees. The regression coefficient file is an array of 81*110 * (3*L+1+9), where L(=101) is the atmospheric pressure levels used in RTM.
The following equation is used to derive TPW:
pw = 1000 which means the water density in kg/m3
g = 9.8 which means the gravity acceleration in m/s2
q(p) = the mixing ratio (g/kg) of water vapor profile at pressure level p
ps = is the surface air pressure in hPa
Since the water vapor content is very rare above 300 hPa, only water vapor content between surface and 300 hPa is accumulated to derive TPW.
Layer precipitable water (PW) provides information on the water vapor contained in a vertical column of unit cross-section area in three layers in the troposphere:
Boundary Layer (BL): [Surface - 900 hPa]
Middle Layer (ML): [900 hPa - 700 hPa]
High Layer (HL): [700 hPa – 300 hPa]
In some cases, such as the center of a low pressure system the surface air pressure could be lower than 900 hPa. In other cases such as over the high altitude areas, the surface pressure can get lower than 700 hPa. The sigma pressure ordinate is applied to circumvent such cases. 1
1Li, Jun, Timothy J. Schmit, Xin Jin, and Graeme Martin. NOAA NESDIS Center for Satellite Applications and Research GOES-R Advanced Baseline Imager (ABI) Algorithm Theoretical Basis Document: Legacy Atmospheric Moisture Profile, Legacy Atmospheric Temperature Profile, Total Precipitable Water, and Derived Atmospheric Stability Indices v.2.0. September 2010. http://www.goes-r.gov/products/ATBDs/baseline/Sounding_LAP_v2.0_no_color.pdf