Cloud Phase Determined by GOES-16 Brightness Temperature Differences

March 16th, 2017 |

Channel Difference Field (8.4 µm – 11.2 µm), 2027 UTC on 16 March 2017 (Click to enlarge)

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

One of the GOES-16 Band Difference Products available in AWIPS is shown above (click here for the same image with a default enhancement), the 8.4 µm – 11.2 µm ‘Cloud Phase’ Channel Difference. There has been considerable work showing a good correlation between the 8.4 µm – 11 µm brightness temperature difference and cloud-top phase. Click here for example. The key take-aways:

  1. “Radiative transfer simulations indicate that the brightness temperature difference between the 8.5- and 11-micron bands (hereafter denoted as BTD[8.5-11]) tends to be positive in sign for ice clouds that have an infrared optical thickness greater than approximately 0.5. Water clouds of relatively high optical thickness tend to exhibit highly negative BTD[8.5-11] values of less than -2K.”
  2. “Clear-sky BTD[8.5-11] values tend to be negative because the surface emittance at 8.5 microns tends to be much lower than at 11 microns, especially over non-vegetated surfaces.”
  3. “Small particles tend to increase the BTD[8.5-11] values relative to large particles because of increased scattering.”

This Algorithm Theoretical Basis Document (ATBD) contains further information and references on the topic.

In the color enhancement above (generated using just 3 colors — blue, red and yellow, and easily changeable for those whose eyesight is color challenged), negative brightness temperature differences — ice clouds — are denoted by red to yellow values. Positive values are blue. Water-based clouds are white or light blue, ice clouds are red. Large Brightness Temperature Differences occur over the Desert southwest and strong negative values (blue in the enhancement) are present because of emissivity differences from the soil at the two wavelengths. The toggle below cycles through the Band Difference field, the 8.4 µm and 11.2 µm imagery, the upper level water vapor (6.19 µm), the cirrus channel (1.378 µm) and the Veggie channel (0.86 µm).  Click here for a toggle between the Cloud Phase Product and Water Vapor and Cirrus channels only (to highlight ice clouds), or here for a toggle between the Cloud Phase and Veggie Band (a band in which clouds composed of water droplets are visible).

One of the GOES-16 Baseline Products will be Cloud Phase. A beta version of this product should be flowing before the end of May. The ATBD for that product shows that both 8.4 µm and 11.2 µm data are used in its creation, and the channel difference shown here shows why.

Cloud Phase Brightness Temperature Difference (8.4 µm – 11.2 µm), Window Channel (11.2 µm), Infrared Cloud Phase (8.4 µm), Upper Level Water Vapor (6.19 µm), Cirrus Channel (1.38 µm) and Veggie Band (0.86 µm), all at 2027 UTC on 16 March 2017 (Click to enlarge)

Fact Sheets are available for the 8.4 µm and 11.2 µm Channels on GOES-16 from the GOES-R website.

AWIPS Notes: AWIPS sometimes mislabels the 8.4 µm channel as 8.5 µm. The Channel Difference field shows missing data where the brightness temperature difference field is exactly zero. Such points are apparent in the image above over Minnesota and North Dakota as black speckles.

GOES-16 visible and thermal signatures of Space-X EchoStar 23 rocket launch

March 16th, 2017 |

GOES-16 Visible (0.64 µm, left), Near-Infrared (1.61 µm, center) and Shortwave Infrared (3.9 µm, right) images [click to enlarge]

GOES-16 Visible (0.64 µm, left), Near-Infrared (1.61 µm, center) and Shortwave Infrared (3.9 µm, right) images [click to enlarge]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

Visible and thermal signatures of the Space-X EchoStar 23 rocket launch were seen with GOES-16 imagery on 16 March 2017. The set of 3 images above consists of 5-minute CONUS sector scans at 05:54:33 UTC (about 5 minutes before launch), 05:59:33 UTC (around launch time) and 06:04:33 UTC (about 5 minutes after launch). The 05:59:33 UTC image was actually scanning the NASA Kennedy Space Center (station identifier KXMR)  area at 06:00:38 UTC, just after the 06:00 UTC launch time. A faint bright glow of the rocket booster was seen on the 0.5-km resolution Visible (0.64 µm) image; the 1-km resolution Near-Infrared (1.61 µm) rocket signature was much brighter, because this spectral band senses radiation from both visible and infrared portions of the electromagnetic radiation spectrum (which of the two was a stronger contributor to the bright signal is difficult to determine); the 2-km resolution Shortwave Infrared (3.9 µm) image displayed a warm (dark black enhancement) “hot spot”, although it was not exceptionally warm (with a 306.8 K maximum brightness temperature).

A “warm signal” was also observed on the three GOES-16 ABI Water Vapor bands: Lower-Level (7.3 µm), Mid-Level (6.9 µm) and Upper-Level (6.2 µm), as shown below. While water vapor is certainly a by-product of rocket booster combustion, it is important to remember that the Water Vapor bands are first and foremost Infrared bands that sense the brightness temperature of a layer of moisture (which can vary in both altitude and depth, depending on the temperature/moisture profile of the atmosphere and/or the satellite viewing angle). In this case, the atmosphere was relatively dry over the region, with little moisture aloft to attenuate the rocket signature — shifting the roughly-corresponding GOES-13 Sounder (had the GOES-13 Sounder instrument been operational)  water vapor weighting functions (available from this site) to lower altitudes. However, moisture considerations aside, the rocket signature seen on the 05:59:33 UTC water vapor imagery was primarily a thermal anomaly.

GOES-16 Lower-Level Water Vapor (7.3 µm, left), Mid-Level Water Vapor (6.9 µm, middle) and Upper-Level Water Vapor (6.2 µm, right) images [click to enlarge]

GOES-16 Lower-Level Water Vapor (7.3 µm, left), Mid-Level Water Vapor (6.9 µm, middle) and Upper-Level Water Vapor (6.2 µm, right) images [click to enlarge]

McIDAS-V images of GOES-16 Near-Infrared (1.6 µm and 2.2 µm) and Shortwave Infrared (3.9 µm) data at 05:59:33 UTC (below; courtesy of William Straka, SSEC) provided another view of the rocket launch signature.

GOES-16 Near-Infrared (1.61 µm and 2.2 µm) and Shortwave Infrared (3.9 µm) images [click to enlarge]

GOES-16 Near-Infrared (1.61 µm and 2.2 µm) and Shortwave Infrared (3.9 µm) images [click to enlarge]