Satellite Observations

Retrievals of aerosol and trace gas information from current research and operational satellites have great potential to assist in several of the TexAQS/GoMACCS science objectives. Instruments on NASA and NOAA satellites are currently able to observe several of EPA's criteria pollutants (Table 7). While polar-orbiting satellites (e.g., MODIS) provide coverage once a day globally, geostationary satellites (e.g., GOES) provide coverage over the continental United States once every fifteen minutes. A multiple platform and sensor approach, integrating in situ and satellite data with modeling, might be essential to address TexAQS/GoMACCS science objectives.

NOAA and NASA satellites and their measurement capabilities:

Satellite Platform Instruments Some key data products Vertical Resolution
NASA Aura TESCO, CH4, O3, HNO3, NO2Trop. column/4 km
OMIO3, NO2, SO2, H2CO, aerosol optical depth, aerosol typeTrop. column
NASA Aqua MODIS*Aerosol optical depthTrop. column
AIRS*COTrop. column
AIRS*Aerosol optical depthTrop. column
NASA Terra MOPITTCOTrop. column
MISRAerosol optical depth, aerosol typeTrop. column
MODIS*Aerosol optical depthTrop. column
NASA CALIPSO CALIOPAerosol backscatter ratioTrop. vertical profile
NOAA GOES ImagerAerosol optical depth (30 minute interval)Trop. column (land and water)
NOAA N16, N17, N18 AVHRRAerosol optical depthTrop. column, (water only)
NOAA GOES ImagerShortwave flux (hourly)Surface
ImagerUV (erythemal) flux (hourly)Surface
NASA CERESShortwave and longwave fluxTop of the atmosphere; surface

* Available through NOAA in near real time

Although satellite data has some disadvantages compared with other means of observing ozone and aerosols, the advantages of including satellite information currently outweigh the disadvantages. Accuracies of satellite retrieved aerosol optical depths and trace gases are not as good as measurements made from ground because satellite retrievals tend to have higher uncertainties. These uncertainties are associated with converting slant column retrievals to column amounts and isolating the tropospheric column from the total column in the case of trace gases. For aerosol retrievals, difficulties in modeling aerosol type and variability in surface reflectance lead to large uncertainties. Nevertheless, while the ability to measure trace gases and aerosols at the desired spatial resolution, temporal resolution, and accuracy might not be realized for several years, the benefits of exploiting these measurements for air quality studies are so substantial that the validation required to exploit them should be pursued immediately.

Satellite data of aerosols and trace gases have three potential applications for the TexAQS/GoMACCS field campaign:

Using the satellite data in near real time:

  • Image loops (especially from GOES) for aircraft/ship flight deployment
  • Comparisons with in situ measurements
  • Assimilation into forward trajectory models to forecast plume location

Retrospective looks at the data collected during TexAQS/GoMACCS:

  • Comparisons of satellite and ground/aircraft/ship based measurements of various parameters
  • Validation of satellite retrievals using in situ measurements. Assessment of uncertainties in the retrieval algorithms due to various assumptions. Reprocessing of satellite data with assimilated field measurements.
  • Extending the spatial (horizontal) dimension for studying problems such as contributions of long range transport to local air quality

Using the satellite data in modeling studies:

  • Verifying chemistry and transport model forecasts with satellite data
  • Diagnosing sources of uncertainties in chemistry and transport models
  • Assimilating satellite data to improve initial and boundary conditions in the models
  • Radiative effects of aerosols