Effects of a ship's motion on the measurements of vertically pointing radars: the scientific basis and development of radar-based VAPs for the MAGIC AMF deployment

Poster PDF

Description

The second ARM Mobile Facility was created with the intent to include deployments in marine environments. After initial land-based deployments in Steamboat Springs, Colorado, and Gan Island, Maldives, the first deployment at sea began in October 2012. The year-long MAGIC deployment consists of approximately 20 round-trip transects between Los Angeles, California, and Honolulu, Hawaii. Among the many challenges associated with this deployment is determining the impact of the ship's motion on the measurements of the vertically pointing radars. Development of two post-processing value-added products (VAPs)—“kazrshipcor1” VAP and the “mwacrshipcor1” VAP—is necessary to provide adjustments for the movement of the ocean-going ship.

The “kazrshipcor1” VAP will post-process data from the unstabilized Ka-band ARM zenith radar (KAZR). Since KAZR is unstabilized and will move with the ship, the radar beam will typically be off-zenith due to ship roll and pitch. This creates the need for two corrections: the radar range coordinate will often differ from the earth-based vertical height above the radar, and observed mean Doppler velocities will often not be vertical velocities. The “kazrshipcor1” VAP will provide a time-varying height coordinate corresponding to the Earth-based vertical location of each radar range gate above sea level. It will also perform a geometric correction to the radar’s radial velocities to transform them to the Earth-based vertical coordinate. The VAP will also adjust for the height and velocity biases caused by the ship’s time-varying height (heave) and vertical velocity (heave velocity). An exploration of the influence that horizontal winds may play on radar-measured radial mean Doppler velocities will be included.

The “mwacrshipcor1” VAP will post-process data from the stabilized marine W-band ARM cloud radar (M-WACR). Placement on a stabilized platform ensures that the M-WACR will be collecting data at vertical incidence. First-order adjustments to the mean Doppler velocities will only require correction for ship heave velocity. A time-varying height above sea level coordinate will be produced, reflecting the time-varying ship heave. However, in the event of a known failure of the stabilized platform, M-WACR velocity observations and measurement heights can be corrected for roll and pitch-related offsets from vertical, similar to those from KAZR.