Instrument: ER-2 X-band Doppler Radar (EXRAD)

 

Figure 1: Diagram of EXRAD Hardware onboard the ER-2

(Image source: GSFC EXRAD webpage)

 

Weather radars use electromagnetic radiation to detect meteorological targets in the atmosphere. EXRAD transmits radiation at a frequency of 9.6 GHz (X-band), which gives it high-sensitivity to precipitation while also maintaining the ability to penetrate the precipitation without extensive attenuation. In addition, X-band is ideal for airborne observations because the relatively small wavelength allows for a smaller antenna diameter that is more suitable for operation on an aircraft. EXRAD’s Doppler capabilities allow it to measure the velocity of air motions within precipitation. The conical/cross-track scanning antenna enables the calculation of horizontal winds flowing along and across the aircraft flight path, provides a wider field-of-view for observations, and allows the characteristics of precipitation particles such as orientation and phase to be determined. The nadir-pointing beam measures vertical motions beneath the plane using the vertical velocities of precipitation particles. Together, the dual-beam measurements allow the 3-dimensional structure of precipitation and winds below the plane to be constructed (Figure 2). These EXRAD data are used to improve and validate satellite precipitation estimates and to examine various weather phenomena such as convective precipitation systems and tropical cyclones.