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ASAP NPOESS Aviation Assessment Benchmark Report Highlights


image Since its inception in 2002, the NASA Applied Sciences Aviation Program has identified or developed a number of successful ASAP applications for advanced imagers, such as the Moderate Resolution Spectroradiometer (MODIS), and advance sounders, such as the Atmospheric Infrared Sounder (AIRS). Application utility in the detection and characterization of diverse aviation weather hazards ranges from in-flight icing to convective weather to airborne volcanic ash which motivated the program to undertake an assessment of the National Polar Orbiting Environmental Satellite System (NPOESS) Program. This assessment was made to determine the impact the system will have on future aviation applications development and to examine the ramifications of program cutbacks mandated by the Nunn-McMurdy Act review of the NPOESS program in 2006. The Nunn-McCurdy Program Review has significant impact on the role of NPOESS in aviation weather, but the new “certified” program will still provide significantly enhanced observational resources for aviation applications.

The number of satellite platforms has been reduced from six to four, with EUMETSAT’s METOP satellite replacing the mid-morning NPOESS slot. Only a single CrIS and ATMS instrument will be deployed on NPOESS. NPOESS will be particularly valuable over northern (Alaska) and polar regions, but also useful globally. Although several imager spectral bands are missing as compared with current operational/research instrumentation, VIIRS will provide low-light imaging capability, near uniform nadir to limb horizontal resolution, and improved temporal latency. Therefore, many of the current ASAP applications and other satellite-based aviation algorithms may have to be modified to support the VIIRS instrument. CrIS will provide an additional hyperspectral platform to characterize atmospheric stability and should provide enhanced forecasting information at high latitude aviation routes where the volcanic ash threat is significant. With the current timeline, the first NPOESS launch is expect in FY2009. NPOESS will provide great enhancement to observational capabilities to support aviation, and the community is looking forward to its availability.



Specific Improvements Expected with NPOESS Deployment

VIIRS
  • Consistent nadir to limb cross track resolution to allow application utility over a larger domain.
  • Day-Night-Band providing diurnal detection of volcanic ash, cloud phase, fog, and convection unique to current civil (research or operational) imager instruments.
  • True color imagery allowing rapid qualitative human interpretation of aviation hazards (volcanic ash plumes, convective initiation, fog, etc.).
  • Dual band gain bands should provide improved dynamic range detection over high contrast and low contrast radiance scenes.
  • Improved time latency so global products are available at the major weather centers for model input and decision support applications in no more than 30 minutes.

CrlS
  • Provides another hyperspectral instrument to improve vertical resolution for globally sounding the atmosphere.
  • Coupled with AIRS and IASI, improved retrieval of wind fields at high latitudes and volcanic ash location and heights should be realized.
  • More continuous coverage of land-based stability and location of low and mid-level moisture will provide more accurate location of potential convective instability.



Deficiencies, Gaps and Shortfalls in NPOESS

Data Availability and Latency:

Polar satellites traditionally have two modes of disseminating data and imagery: a direct, real-time transmission that can only be received by suitably equipped stations within view of the satellite overhead, and by high-speed play back recorded data when passing within range of a special, high-end satellite facility. For use with numerical models, the only way to obtain full global data sets has been to wait and have the data relayed from a suitable satellite center capable of down-linking the recorded data. With a limited number of receiving stations there have often been delays of up to several hours between the observations and their availability for use.

For the NPOESS constellation of satellites a much improved data acquisition system termed the “Safety Net” will use as many as 15 unmanned receiving stations spread around the globe, with each site having access to high-speed international land lines for transmitting the satellite observations to civilian and military weather centers. Through this system, it is expected that 95% of the observations will reach the designated weather centers within 30 minutes of the data collection. While this is a vast improvement over the current POES and DMSP systems, it may not meet aviation requirements for rapid access. Instead, there may be a requirement for direct read-out stations capable of receiving the real-time data transmissions located in sites that can be used to generate aviation specific weather products or transmit the observations to central aviation centers.

With the incorporation of METOP satellites into the future NPOESS operational system, there will have to be additional attention paid to rapid data collection and dissemination, with the potential for receiving stations to be equipped with separate NPOESS and METOP receiving stations.

Aviation weather hazards evolve rapidly and will require unusually rapid access to the observations that may not be met by the currently proposed dissemination system.


Spectral Coverage:

VIIRS will have some spectral limitations, such as the lack of 14.3 – 13.21 µm CO2 temperature absorption bands and 7.51 - 6.89 µm water vapor bands. The lack of spectral coverage on VIIRS will affect some of the derived meteorological products capable of extraction from MODIS, such as CO2 slicing cloud top altitude (important for accurate cloud altitude assignment for high cirrus clouds). In addition, accurate high level clouds heights will be hard to achieve without CO2 absorption channels. The lack of water vapor bands will impact winds derived from tracking water vapor features over the polar regions and the inference of turbulence estimates now possible using MODIS imagery. The 7.3 µm SO2 channel will also not be present, which is important for tracking volcanic ash SO2 plumes.

While spectral gaps exist within the CrIS infrared spectrum compared with IASI, they do not significantly impact aviation related applications developed using AIRS, NAST-I, and S-HIS technologies such as volcanic ash SO2 detection, water vapor imaging and CO2 slicing.


Variable Payloads:

Introducing METOP into the NPOESS constellation is logical and bodes well for future U.S.-European cooperation. METOP, however, was designed to complement the current generation of POES satellites and not NPOESS. This change is likely to require an extensive series of negotiations that may require changes in both the NPOESS and METOP instrument configurations.

Most notably, the older technology AVHRR/3 is not a good substitute for VIIRS. In addition, Combining METOP and NPOESS will also present significant problems with data access, essentially requiring parallel data acquisition and distribution systems. Even instruments that have quite similar capabilities, such as IASI and CrIS, may well present difficulties for assimilation at different times into a single operational model.

Despite these problems, some benefits for METOP-NPOESS cooperation are noted. IASI appears to be quite comparable with the CrIS hyperspectral sounding system, and having both in orbit will allow extensive testing of each design, perhaps resulting in the adoption of one of the two designs for both METOP and NPOESS in the later satellites to be launched. Similarly, the AMSU on METOP may ultimately be replaced by the U.S. ATMS after it is validated and experiences a period of operational testing. The European advanced scatterometer (ASCAT) will help fill in for the cancelled CMIS instrument, particularly with its capability of monitoring ocean wind speed and direction, until a less ambitious replacement makes its way to the U.S. satellite system. Finally, using the older SEM-2 on both METOP and NPOESS will provide seamless monitoring of the space environment, but with no advancement over current capabilities.

Other sensors eliminated from the NPOESS core program are expected to be shifted to other NASA or DoD satellites with some cost-saving for the NPOESS program, but will not necessarily result in any significant reduction in the total U.S. government costs if another funding source is found. And in one case, an existing NASA research instrument (CERES) will fill in for the cancelled ERBS on the NPOESS C1 satellite.


Direct Integration of NPOESS Aviation Requirements:

The aviation community was not part of the EDR process for NPOESS. This lack of input has produced some problems with applying heritage satellite aviation application algorithms to VIIRS. The EDR selection process has been modified to include aviation specific components for future sensor development such as requirements for GOES-R Advanced Baseline Imager (ABI) (Schmit et al., 2005). It is important for the aviation community to be represented because trans-ocean and upper latitude aviation weather needs are highly dependent on satellite data and NWP models initialized with satellite data. Satellite data will be especially important when NGATS is implemented throughout CONUS.

Potential Future Enhancements

For aviation applications time latency and temporal/spatial resolution drive the utility of the products for nowcasting. Any improvement of satellite aviation weather product availability before decision support systems should result in an increased ability to avoid aviation hazards and economic savings. With the implementation of fiber optic data transmission, computer processing power, and advanced relay ground stations, potential improvement in temporal latency should be achieved in the future.

Because most satellite applications have been developed using heritage operational and research imagers, the addition of CO2 temperature and 6.7 µm water vapor bands to the VIIRS instrument is essential for many satellite aviation applications. The CO2 temperature bands provide more accurate cloud height assignments and cloud detection. The water vapor band is essential for detecting turbulence waves and clouds.

International coordination of satellite programs is essential, especially for polar orbiting systems to provide consistent assets for improved instrument synergy. Polar orbiting satellites with inconsistent spectral ranges and scanning strategies mitigate potential collaborative measurement capabilities that may provide more value than any instrument. For instance, AVHRR/3 and VIIRS are not a feasible match for combined wind retrieval at polar regions.

When satellite programs are developing Environmental Data Requirements (EDR), the aviation community should play a role in defining aviation specific needs such as volcanic ash detection, icing potential, convective initiation and turbulence interest field detection. It is difficult to retroactively fit mature satellite aviation application algorithms for spectral regions not optimal for specific hazard detection. This has just recently been recognized within the NOAA GOES-R program, and some aviation needs are being directly addressed within the system requirements document.






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