The Community Satellite Processing Package (CSPP) allows a user to manipulate VIIRS data to create high-quality, full-resolution imagery (see, for example, this I05 example, and this Day Night Band example, and this I01 example). In addition to single-band images, imagery for products such as Advanced Clear Sky Processor for Ocean (ACSPO) sea-surface temperatures (SSTs) can also be created, as shown above. Polar2grid software is being used for all examples in this blogpost. It is a Linux-based software package that is available for free download here.

ACSPO SST data derived from VIIRS data are available online here (for Suomi-NPP) and here (for NOAA-20). Data files appear about 1-3 days after observation (a user with a Direct Broadcast antenna, of course, can process data for the needed SST files in near-real time); the two files I downloaded (from this source directly; it is also accessible via NOAA CLASS — see the note at the NOAA CLASS website and click through to the NOAA-20 site) include 10 minutes of VIIRS ACSPO observations from NOAA-20: from 09:00:00 to 09:09:59 and from 21:30:00 to 21:39:59) on 21 November 2023. This map (from this source) shows that the observations are over the Arabian Sea. The downloaded files have a file naming structure shown below

20231121090000-OSPO-L2P_GHRSST-SSTsubskin-VIIRS_N20-ACSPO_V2.80-v02.0-fv01.0.nc
20231121213000-OSPO-L2P_GHRSST-SSTsubskin-VIIRS_N20-ACSPO_V2.80-v02.0-fv01.0.nc

Several steps are needed before the imagery shown above is created. First, I defined a grid using Polar2Grid software (that is, p2g_grid_helper.sh) onto which the data are placed, because the orbit paths at 0900 and 2130 do not sample the same domain. That command is shown below.

$POLAR2GRID_HOME/bin/p2g_grid_helper.sh Arabian 63.5 14.6 2000 -2000 1440 1120 > $POLAR2GRID_HOME/Arabian.yaml

Because I know beforehand the range of sea-surface temperatures that are likely in November in the Arabian Sea, I can instruct (via a yaml file that I named “my_sst_rescale.yaml“) Polar2Grid to scale the computed SSTs appropriately. The contents of the file, that I placed in $POLAR2GRID_HOME/bin, are shown below. I’m constraining the temperatures to be between 15^oC and 35^oC.

enhancements:
  oman_sst:
    standard_name: sea_surface_subskin_temperature
    operations:
      - name: linear_stretch
        method: !!python/name:satpy.enhancements.stretch
        kwargs: {stretch: 'crude', min_stretch: 288.16, max_stretch: 308.16}

The polar2grid commands to (1) create the .tif file (run from the $POLAR2GRID_HOME/bin directory) is below, and (2) to apply a colormap to the two tif files (one at 0900, one at 2130) are shown below; the wildcard ‘20231121???0’ in the file name resolves the files containing both 0900 and 2130 UTC data. The two filenames created are shown beneath the polar2grid command. The add_colormap.sh command overwrites the .tif file, adding colormap information from the file p2g_sst_palette.txt, a colormap that is supplied with the polar2grid installation; a user could, of course, alter the colormap to something of their own choosing.

$POLAR2GRID_HOME/bin/polar2grid.sh -r acspo -w geotiff -p sst -g Arabian --grid-configs $POLAR2GRID_HOME/Arabian.yaml --fill-value 0 --extra-config-path my_sst_rescale.yaml -f /path/to/J01Data/20231121???0*SST*N20*

noaa20_viirs_sst_20231121_090000_Arabian.tif
noaa20_viirs_sst_20231121_213000_Arabian.tif

$POLAR2GRID_HOME/bin/add_colormap.sh $POLAR2GRID_HOME/colormaps/p2g_sst_palette.txt noaa20_viirs_sst_20231121_???000_Arabian.tif

The imagery above includes coastlines, borders, and a labeled colorbar. Those are all added with the following commands, one for each time.

$POLAR2GRID_HOME/bin/add_coastlines.sh --add-coastlines --add-borders --add-grid --grid-D 10 10 --grid-d 10 10 --grid-text-size 16 --add-colorbar --colorbar-text-color "white" --colorbar-text-size 20 --colorbar-title "N20 VIIRS ACSPO SST 21 November 2023 0900 UTC" --colorbar-height 32 --colorbar-tick-marks 4 --colorbar-min 15.0 --colorbar-max 35.0 --colorbar-units "°C" noaa20_viirs_sst_20231121_090000_Arabian.tif

$POLAR2GRID_HOME/bin/add_coastlines.sh --add-coastlines --add-borders --add-grid --grid-D 10 10 --grid-d 10 10 --grid-text-size 16 --add-colorbar --colorbar-text-color "white" --colorbar-text-size 20 --colorbar-title "N20 VIIRS ACSPO SST 21 November 2023 2130 UTC" --colorbar-height 32 --colorbar-tick-marks 4 --colorbar-min 15.0 --colorbar-max 35.0 --colorbar-units "°C" noaa20_viirs_sst_20231121_213000_Arabian.tif

Note the warmer temperatures during the daytime (i.e., at 0900 UTC). The difference between day and night will be especially pronounced in regions of reduced vertical mixing in the ocean (that is, light winds), and MetopB ASCAT winds on the 21st (below, from here) do show light winds over much of the Arabian Sea early on the 21st.

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A series of LightningCast Probability plots from this RealEarth-powered website, below, shows increasing probabilities of lightning over the South Pacific to the south of American Samoa’s Manu’a Islands. The 75% contour (magenta) appears at 0530 UTC; the first GLM observation is shown at 0620 UTC. LightningCast is the probability that a GLM observation will occur within the next 60 minutes, so this is a good case showing its efficacy.

The WSO forecast office in Pago Pago was using this product to advertise the danger from lightning, as shown in the screenshot below for their Facebook page (direct link to the image). The time of the image below (ca. 0826 UTC) is after the end of the animation above; the lightning with this convective complex continued for several hours.

GOES-18 Level 2 products below (Lifted Index, left, scaled from -5 to 10 and Total Precipitable Water, right, scaled from 1 to 2.5 inches) show that the convection developed in a region where TPW and instability were both increasing to the north. Knowledge of the distribution of these level 2 products in concert with the development of LightningCast probabilities is a good indicator that convection will develop. The convection that developed eventually overspread Tutuila; the airport at Pago Pago received more than 0.5″ of rain.

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Overlapping 1-minute Mesoscale Domain Sectors provided 30-second interval GOES-16 (GOES-East) images from all 16 of the ABI spectral bands plus a Rocket Plume RGB (above) — which displayed signatures of the SpaceX Starship 2 rocket that was launched from the Starbase facility in Boca Chica Beach, Texas at 13:02:53 UTC on 18 November 2023. The Stage 1 rocket booster condensation cloud was evident in images from all 16 spectral bands, as it began to drift slowly southeastward away from the Texas coast — and the ascending rocket booster’s thermal signature was seen in Near-Infrared and Infrared spectral bands 03-16, as well as the Rocket Plume RGB.

A close-up view using 16-panel displays of all GOES-16 ABI spectral bands (below) showed that a reflectance signature of the Stage 1 rocket booster was evident in most of the Visible and Near-Infrared bands (01/02/03/05/06) at 13:02:55 UTC, along with a warm thermal signature in Infrared bands 07 and 11-15. After that time, warm thermal signatures then became apparent in all Near-Infrared and Infrared spectral bands (03-16) as the rocket began its ascent.

A larger-scale look at GOES-16 Upper-level Water Vapor (6.2 µm), Mid-level Water Vapor (6.9 µm), Low-level Water Vapor (7.3 µm) and Rocket Plume RGB images (below) allowed a signature of the Stage 2 rocket booster to be followed farther east across the Gulf of Mexico.

In a series of toggles between GOES-16 Upper-level Water Vapor (6.2 µm) and Shortwave Infrared (3.9 µm) images at 13:05:25 UTC, 13:06:25 UTC, 13:07:25 UTC and 13:09:25 UTC (below) a small cluster of warm 3.9 µm pixels (darker shades of orange-red) marked the exit point of hot exhaust from the Starship booster engines — and in 6.2 µm images, the trailing exhaust plume extended southwestward then westward from those warm 3.9 µm pixels. Note the change in exhaust plume shape with time and atmospheric layer: at altitudes of 61-101 km (where the Mesosphere and lower Thermosphere had more density, and higher ambient pressure), the plume was more linear — but at higher altitudes of 128-149 km (where the Thermosphere was much less dense, with lower ambient pressure) the plume was able to expand outward into more of a curved shape.

Thanks to Todd Beltracci, The Aerospace Corporation, for his analysis of Starship 2 test flight telemetry and how it related to the various GOES-16 image features.

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The Solar Ultraviolet Imager (SUVI) on GOES East captured a partial solar eclipse during the new moon on November 13th. But the moon’s shadow didn’t reach Earth. Why’s that?

Solar eclipses are only possible when the new moon occurs near the nodes of the lunar orbit, which is where the moon’s path intersects with the Sun-Earth ecliptic plane. This alignment makes it possible for the moon’s shadow to reach Earth’s surface and cause an eclipse.

Lunar nodes only align with the Sun-Earth line twice a year. The time on either side of that alignment is often called an “eclipse season.”  

Turns out geosynchronous satellites, which orbit Earth 22 thousand miles above the equator (several Earth diameters high) can pass through the lunar shadow during an eclipse season without the moon’s shadow reaching Earth, essentially meaning satellites have longer eclipse seasons than Earth.

Monday November 13 marked one lunar cycle since the October annular eclipse on Earth, so SUVI was within an extended satellite eclipse season and able to track the moon transiting the Sun from geostationary orbit.

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