Satellite-based Nowcasting and Aviation Program


Instrument

Observation Validation

Validation of remotely sensed observations of atmospheric, dynamic and thermodynamic properties is extremely important for the proper understanding and utilization of these products. Three primary validation areas have been addressed within the SNAAP program. See the “Publications” and “Presentations” links for the latest results from these studies.

Aircraft in-situ Measurement of Temperature, Moisture, and Wind

The accuracy of weather forecasts is largely dependent on reliable vertical profiles of meteorological data such as temperature, moisture, and wind. These profiles may be acquired from weather balloons, however, the scarcity of weather balloon data in both space and time poses a problem. To attain a greater number of meteorological profiles, instruments have been deployed aboard some commercial aircraft. Two such instruments are TAMDAR (Tropospheric Airborne Meteorological Data Report) and WVSS-II (Water Vapor Sensing System).

The TAMDAR instrument measures temperature, moisture, icing, turbulence, and wind speed and direction. TAMDAR sensors have been mounted on 64 MESABA Airlines Saab 340 commuter planes. One advantage of mounting these instruments on small commuter aircraft is that these aircraft travel to many small airports, while larger jet aircraft will generally travel only between a few large airports. UW-CIMSS deployed its mobile instrument laboratory (the AERIbago) to Memphis, TN on two occasions for validation purposes. About 55 TAMDAR profiles are collected daily at Memphis, a MESABA Airlines hub. The goal of these experiments was to provide a ground-truth assessment of the accuracy of the TAMDAR instruments by comparing the temperature, moisture, and wind profiles to co-located rawinsonde data.

The WVSS program has focused on developing moisture sensors to be mounted on jet aircraft. During the past decade, the WVSS has evolved from using a radiosonde-like thin-film capacitor relative humidity sensor (WVSS-I) to a more precise laser diode mixing ratio measurement system (WVSS-II). WVSS-II instruments are currently deployed on UPS Boeing 757 aircraft. Similar to the TAMDAR validation, UW-CIMSS deployed the AERIbago to the Kentucky Air National Guard facility, adjacent to the Louisville Airport, where many UPS aircraft arrive/depart nightly. Between 25 and 30 WVSS-II instruments were mounted and operational during the experiment. The WVSS-II data was compared to co-located rawinsonde data using the same methodology as the TAMDAR validation.

Satellite-Derived Winds

Satellite-derived winds are also being validated through the SNAAP program. Satellite winds are used in a wide variety of meteorological applications such as NWP model data assimilation, tropical cyclone analysis and forecasting, and convective weather nowcasting. Thus, it is important to understand the error characteristics of the remotely sensed wind estimates, such that they can be effectively understood and properly utilized within these applications. Within the SNAAP program, NOAA/NESDIS operational and CIMSS experimental mesoscale winds from the GOES-12 instrument are compared against rawinsonde and NOAA Wind Profiler Network observations over the ARM Southern Great Plains Central Facility. The objective of this work is three-fold:

  1. To evaluate the feasibility of using 6-minute resolution Wind Profiler observations as a “truth” standard for wind validation
  2. To understand the natural spatial and temporal variability of atmospheric winds throughout the troposphere
  3. To understand the speed, direction, and height assignment characteristics of satellite winds over a variety of cloud types and flow regimes.

Satellite-Derived Cloud Products

Another research area within the SNAAP program is the detailed assessment of clouds and their properties (e.g. clear/cloud scene identification, cloud type, and cloud top height) The aviation industry relies on such assessments for the development and execution of safe flight plans. One focus has been on developing detailed cloud products for use over the continental United States (CONUS) at high temporal and spatial resolutions. These products (effective cloud amount and cloud top height) make use of data from the GOES-10 (western US) and GOES-12 (eastern US) Sounder and Imager instruments. Cloud top height is derived using a combined CO2 ratio (used primarily for high clouds) and infrared window (used primarily for low and mid-level clouds) technique. Validation efforts within SNAAP have examined the accuracy of satellite-derived cloud top height products using Cloud Physics Lidar (CPL) data taken during the Atlantic-THORPEX Regional Campaign (ATReC) as reference data set. Using airborne lidar data provides the advantages that the cloud top heights are measured rather than derived, as they are when ground based data are used.