- ProDA Web Application
We have designed and developed a system, called PRODA, which deploys wavelet transform for efficient range-aggregate query processing. Typically, wavelet transform is utilized to reduce the data size at different resolutions. Unfortunately, data compression methods such as wavelet are only effective on datasets that compress well, and with queries that require the reconstruction of the entire signal. We propose and employ a data-independent approximation technique that is based on query approximation rather than data compression. This approach enables data-independent query processing that rapidly converges to highly accurate result (e.g., 90% accuracy when only 10% of the query is completed). PRODA supports any polynomial range-aggregate query using a single set of pre-computed aggregates.
ProDA Stand-Alone client:
The Genesis GPS Occultation Observations Level 2 data set contains
profiles of atmospheric temperature, pressure, refractivity, and water
vapor pressure with resolution of about a kilometer, derived from
LEO-GPS (low-earth-orbiter satellites and satellites of the Global
Positioning System) radio occultation (limb sounding) data. Similar
profiles from NCEP and ECMWF analyses are also included. LEOs collecting
occultation data include GFZ's CHAMP (CHallenging Minisatellite Payload
satellite) and CONAE's SAC-C. These are the Level 2 products of this
radio occultation data set.
The full set of products available include
CHAMP and SAC-C each carry a JPL Blackjack GPS receiver and a
rearward-facing antenna to record the signals of GPS satellites setting
behind the Earth's limb as the signal passes through the atmosphere.
(SAC-C also carries a forward-facing antenna, currently inactive.)
Typically over 200 of these "occultations" occur per day per LEO with
fairly uniform global distribution. By measuring the precise phase delay
experienced by the GPS signals, and using precise clock-offset and orbit
information, the atmospheric component of the phase delay can be extracted.
Assuming local spherical symmetry about the tangent point, inversion of
the atmospheric phase delay phase measurements during an occultation
yields atmospheric refractivity profiles, which can be converted to
temperature and pressure profiles between 60 km and the middle troposphere,
and, with independent knowledge of temperature, into water vapor density
in the middle and lower troposphere.
Valuable properties of radio occultation measurements of atmospheric
- Level 0: Raw GPS data
- GPS data for orbit determination in RINEX format
- Orbit products
- Level 1A: Atmospheric phase delay and signal amplitude
- Level 1B: Atmospheric doppler shift and bending
- Level 2: Atmospheric refractivity, temperature, pressure, water vapor
pressure profiles, and comparisons to weather analysis and
Comparison of CHAMP and SAC-C to National Center for Environmental
Prediction (NCEP) and the European Center for Medium-range Weather
Forecast (ECMWF) analyses show that GPS occultation temperature profiles
are consistent with the models to better than 0.5 K in the mean, and
better than 1.5 K in standard deviation.
- Self-calibrating, making them ideal for climate detection.
- Sub-kilometer vertical resolution.
- Sub-Kelvin temperature accuracy below 45 km.
- All-weather operation
- Independent height and pressure data allowing computation of
geopotential heights and derived wind fields
- Concurrent global coverage with a small constellation