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EDOP is an X-band (9.6 GHz) Doppler radar nose-mounted in the ER-2. The instrument has two antennas: one nadir-pointing with pitch stabilization, and the other forward pointing. The general objectives of EDOP are the measurement of the vertical structure of precipitation and air motions in mesoscale precipitation systems and the development of spaceborne radar algorithms for precipitation estimation such as will be used for the Tropical Rain Measuring Mission (TRMM).

EDOP measures high-resolution time-height sections of reflectivity and vertical hydrometeor velocity (and vertical air motion when the hydrometeor fall speed and aircraft motions are removed). An additional capability on the forward beam permits measurement of the linear depolarization ratio (LDR) which provides useful information on orientation of the hydrometeors (i.e., the canting angle), hydrometeor phase, size, etc. The dual beam geometry has advantages over a single beam. For example, along-track horizontal air motions can be calculated by using the displacement of the ER-2 to provide dual Doppler velocities (i.e., forward and nadir beams) at a particular altitude.

EDOP is designed as a turn-key system with real-time processing on-board the aircraft. The RF system consists of a coherent frequency synthesizer which generates the transmitted and local oscillator frequencies used in the system, a pulse modulated (0.5 to 2.0 micro-second pulse) high gain 20 kW Traveling Wave Tube Amplifier which is coupled through the duplexer to the antenna, and the receiver which is comprised of a low-noise (~1dB) GaAs preamplifier followed by a mixer for each of the receive channels. The composite system generates a nadir oriented beam with a co-polarized receiver and a 350 forward directed beam with co- and cross- polarized receivers. The antenna design consists of two separate offset-fed parabolic antennas, with high polarization isolation feed horns, mounted in the nose radome of the ER-2. The antennas are 0.76 m diameter resulting in a 30 beamwidth and a spot size of about 1.2 km at the surface (assuming a 20 km aircraft altitude). The two beams operate simultaneously from a single transmitter.

EDOP uses a real-time processor to accommodate the very high data and processing rates required by the system's 4400 Hz pulse repetition frequency. The system obtains high vertical resolution profiles (37.5 meter spacing) of measured quantities. The EDOP system is designed to have both high sensitivity for detection of weaker precipitation returns and a large dynamic range since variations in one vertical profile can exceed 90 dB (including return from the surface). Minimum detectable reflectivity for the system is about -5 dBZ at an altitude of 15 km. In 1997 a new data system was implemented that serves both as a digital IF receiver and a data processing system. This new linear receiver has a wider dynamic range for Doppler measurements as compared with the previous system.

EDOP goals for CAMEX-3 include:

1. Vertical structure of the reflectivity and vertical velocity in the hurricane precipitation region, especially the inner core region and the upper level divergent outflow.
2. Evaluation of TRMM radar algorithms for attenuation and rain rates.
3. The relation of radar-derived vertical circulations to temperature and moisture structure deduced from radiometric measurements.
4. Identification and vertical structure of embedded RmesocylonesS.
5. Deducing microphysical information in hurricanes based on EDOP and microwave radiometer observations.

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