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GOES-R 3.9 um (Channel 7)

GOES-R ABI Fact Sheet Band 7 (“Shortwave Window” Infrared Band)

The “need to know” Advanced Baseline Imager reference guide for the NWS forecaster

By: The Cooperative Institute for Meteorological Satellite Studies (CIMSS)

 

 

The shortwave IR window (3.9 μm) band (on the current GOES imagers) has been demonstrated to be useful in many applications, including fog/low cloud identification at night, fire/hot-spot identification, volcanic eruption and ash detection, and daytime snow and ice detection. Low-level atmospheric vector winds can also be estimated using this band. The shortwave IR window is also useful for studying urban heat islands and clouds. Compared to nighttime, there will be overall warmer temperatures in this shortwave window band during the day, due to the additional reflected solar component.
Source: Schmit et al., 2005 in BAMS, and the ABI Weather Event Simulator (WES) Guide by CIMSS.

 

Figure 1: The Advanced Himawari Imager (AHI) 3.9 μm for Typhoon Maysak from March 31, 2015, at 06 UTC. Credit: CIMSS and JMA

 

In a Nutshell:
GOES-R ABI Band 7 (approximately 3.9 μm central, 3.8 μm to 4.0 μm)
Similar to Suomi NPP VIIRS Bands I4/M12/M13, MODIS Bands 20/21/22/23, AVHRR Band 3, SEVIRI Band 4, AHI Band 7
Available on current GOES (imager and sounder)
Nickname:
“Shortwave window” infrared band
Availability:
Both day and night; during the day contains a reflected solar component
Primary Purpose:
Low fog and stratus, clouds, fires, atmospheric motion vectors, volcanic ash, etc.
Uses Similar to:
At night, other longwave infrared window bands

Table 1: Overview of the 3.9 μm channel

 

Figure 2: MODIS Aqua images from June 22, 2015, of the 11 μm (left panels) and 3.9 μm (right panels) bands. The top images are from 09:55 UTC (nighttime), while the lower panels are from 21:00 UTC (daytime). The fire (or hot spot) near the California/Nevada border (southeast of Lake Tahoe) is evident in the 3.9 μm imagery (Band 22). The 3.9 μm imagery brightness temperatures will generally be greater during the daytime due to additional reflected solar radiation. Fog is along the California coast. The same enhancements are used in each image, with the darker colors representing hotter temperatures. These images were made in McIDAS-V. Credit: SSE

 

Did You Know? To fully understand a spectral band, it’s necessary to consider both its central wavelength and also its spectral width. For example, the current GOES and EUMETSAT imagers both have bands nominally centered at 3.9 μm. Yet, due to their spectral widths, the observed brightness temperatures can be quite different. During the night, the wider EUMETSAT band (approximately 3.6 to 4.2 μm) can be cooler (due to more absorption associated with CO2), yet during the day, the wider EUMETSAT band can be warmer due to more reflected solar energy.

 

GOES-R Baseline Product Used?
Aerosol Detection x
Aerosol Optical Depth  
Clear Sky Mask x
Cloud & Moisture Imagery x
Cloud Optical Depth x
Cloud Particle Size Distribution x
Cloud Top Phase  
Cloud Top Height  
Cloud Top Pressure  
Cloud Top Temperature  
Hurricane Intensity  
Rainfall Rate / QPE  
Legacy Vertical Moisture Profile  
Legacy Vertical Temperature Profile  
Derived Stability Indices  
Total Precipitable Water  
Downward Shortwave Radition: Surface  
Reflected Shortwave Radiation: TOA  
Derived Motion Winds x
Fire / Hot Spot Characterization x
Land Surface Temperature  
Snow Cover x
Sea Surface Temperature x
Volcanic Ash: Detection & Height  
Radiances x

Table 2: List of GOES-R baseline products that use the 3.9 μm channel

 

Ward's Words: Of all of the spectral bands on the GOES-R ABI, Band 7 has the greatest bit depth. That is, the number of discrete values is greater than for the other bands. The reason for this is that Band 7 must be able to sense both very cold features (convective cloud tops) and very hot features (fires). Band 7 will be sent to the Advanced Weather Interactive Processing System (AWIPS) with a depth of 14 bits. The ABI was designed to sense a maximum temperature of 400 K in Band 7. The other ABI bands are delivered to AWIPS with a depth of 12 bits, and a maximum temperature that is lower and more consistent with maximum terrestrial or atmospheric temperatures (between 300 K and 330 K).
Bill “Hima-Ward-i” Ward is the ESSD Chief in NWS Pacific Region and a former Guam forecaster.

 

Figure 3: These images are from MODIS data on June 22, 2015 (09:55 UTC). This is the same time depicted in the panels on the previous page. The left panel is an image of the difference between the 3.9 and 11 μm bands, where negative differences are color-coded, beginning with a value of -1.2 K. The right panel is the GOES-R algorithm IFR (Instrument Flight Rules) probabilities, where higher probabilities are color coded, beginning with 38%. The IFR probability product better characterizes the fog and low clouds than either the band itself or the band difference. Credit: ASPB and CIMSS.

 

ABI Band Approximate Central Wavelength (µm) Band Nickname Type Nominal Sub Satellite Pixel Spacing (km)
6 2.2 "Cloud Particle Size" band Near-IR 2.0
7 3.9 "Shortwave Window" band IR* 2.0

                                                                                                                                                                               * with a reflected daytime solar component

Table 3: Comparison of GOES-R channels

 

Further reading
ABI Bands Quick Information Guides: http://www.goes-r.gov/education/ABI-bands-quick-info.html
CIMSS Fog Product Examples blog: http://fusedfog.ssec.wisc.edu/
CIMSS Satellite blog: http://cimss.ssec.wisc.edu/goes/blog/archives/category/fog-detection
GOES-R COMET training: http://www.goes-r.gov/users/training/comet.html
GOES-R acronyms: http://www.goes-r.gov/resources/acronyms.htm

 

 

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