In-Development / FAQ

FAQ

  • Q: When will the GeoXO Sounder (Geo-S1) launch? To what longitude?
  • A: Currently the GXS is slated for a mid-2030s launch, to approximately 105W. 

  • Q: Do we need both LEO and GEO sounders? 
  • A: Yes, the LEOs (Low Earth Orbiters) are needed to provide global coverage and the geo to provide high temporal and spatial information to improve forecasts of convection. 

  • Q: Was a sounder slated to be on the GOES-R series? 
  • A: Yes. Originally it was called the ABS (Advanced Baseline Sounder) and was designed to work in combination with the ABI (Advanced Baseline Imager). The ABS was renamed the HES (Hyperspectral Environmental Suite), before it was canceled in 2006 (mostly due to budgetary pressures). 

  • Q: Will the GXS be the world’s first geostationary high spectral IR sounder? 
  • A: No. China has two similar sensors in orbit now and Europe will soon have a similar sensor. Other countries are also considering geo sounders.

  • Q: Will hurricane forecasts be improved with GXS information?
  • A: Yes, both OSE (all observed data) and OSSE (all simulated data) experiments have demonstrated significant hurricane track and intensity forecast improvements. 

  • Q: Will land pixels get assimilated for improved weather forecasts?
  • A: Yes, at least pixels with clear skies and known surface emissivity. Cloudy pixels may also be assimilated. 

  • Q: Do we really need >1000 channels since “nobody” assimilates more than a few hundred?
  • A: Yes, we need more spectral bands than imagers provide. In part because NWP is not the only use of these spectra. More channels are needed to reduce the noise. From a practical point of view, even with the current strategies, you can’t select the ~150 channels you want if you don’t start with the full set. Plus, the channel set would depend if you want to focus on temperature or moisture or ozone or surface temperature or clouds or other trace gasses. Finally, Data Assimilation isn’t the only use of GXS radiances, and temperature and moisture vertical retrievals will use many of the observed channels. 

  • Q: Does assimilating principle components avoid this problem [of only being able to assimilate a subset of channels]?  
  • A: Yes, potentially. Using PCs and PC scores inherently includes all channels.

  • Q: Are retrievals not assimilated anywhere yet because their errors are too large or too unpredictable?
  • A: Retrieval errors from “typical” retrievals are hard to characterize and therefore difficult to assimilate.  ECMWF has recently demonstrated assimilation of IASI retrievals done with this goal in mind, and has the same impact as assimilating retrievals.  For water vapor there may be an improvement: https://www.eumetsat.int/assimilation-pc-reconstructed-radiances-nwp“: This study, performed at ECMWF, shows that hyperspectral radiances reconstructed from principle components products can be seamlessly assimilated in an operational system designed for original radiances, preserving the nominal forecast performances. It was performed with IASI operational products, with a specific outlook on the preparation of MTG-IRS.”

  • Q: Can GXS “see through” thick clouds? 
  • A: No, the GXS cannot see through clouds, but it can provide unique spectra of the clouds, which will improve the cloud height retrievals, especially of thin clouds. The assimilation of cloudy radiances is expected well before the launch of GXS. 

  • Q: Can GXS “see through” thin clouds? 
  • A: Yes, GXS can see through some thin clouds or if the footprint is partially cloudy. However, for typical clouds, the GXS cannot see through. GXS can provide unique spectra of the clouds, which will improve the cloud height retrievals, especially of thin clouds.

  • Q: Will GXS provide any trace gas information?
  • A: Yes, the GXS will provide information on ozone, NH3, isoprene, HNO3, N2O and CO. Given that GXS is an infrared sensor, this information will be provided both day and night. GeoXO’s ACX sensor (on the same platform) will work synergistically with the GXS observations for atmospheric composition.
  • Q: Will GXS provide any information on dust plumes?
  • A: Yes, the GXS can also provide information on dust plume characterics.
  • Q: Since GXS is an infrared sensor, does that mean limited impact? 
  • A: No, not at all, since GXS can see between clouds and clouds move and GXS will have repeated looks at a given area. In fact, ECMWF (NOAA Workshop on IR sounders (6 Dec 2021) has shown that hyper-spectral IR sensors allow more positive impact of a given sensor than a MicroWave sensor. (And MW sensors are the backbone for global observations.) Plus, simulations show that GXS will be the dominant sensor for providing information over the contiguous US region, with at least a factor of 2 more improvement than than the next closest sensor. 

  • Q: Will GXS provide atmospheric motion information?
  • A: Yes, the GXS will provide unique atmospheric motion information at many atmospheric levels. The hyperspectral IR data can also input the imager-based cloud height products, especially for high-level clouds.

  • Q: Do we still need geo sounders if we have geo imagers?
  • A: Yes, the images offer limited vertical information on moisture, temperature and very little information on many trace gasses. The GXS will provide unique vertical information compared to a ABI or GXI-like imager, something like 3 to 20 times more information, depending on temperature or moisture and the cloud amount. 

What is the current status?

GXS Concept: from high-spectral infrared radiances to derived products (derived winds and atmospheric instability not shown).