X-band Mobile Radar Data Update Lindsay Bennett and John Nicol

Z Calibration Self-consistency check using Z, ZDR and KDP (Gourley et al. 2009, JTech) Very stringent conditions to avoid effects of attenuation at X-band (i.e. 4-6 degrees of differential phase shift over 10-15 km of light rain) Only suitable data on 17th August (IOP 17) Two half-hour periods indicate a calibration offset of +4.75 dB

ZDR Calibration Based on returns at low elevation angles in light rain, a large ZDR drift during the first two hours of operation was often observed E.g. a ZDR drift of 1.2 dB (from +2.6 to +1.4 dB) on 14th and 17th August Typical ZDR calibration offset = +1.2 dB (+0.2 dB due to small oblate drops)

2-hour drift SELEX identified a problem with the STALO control cable Missing electrical bridge within one connector Prevented the STALO from changing frequency Highlighted an important sensitivity, primarily affecting ZDR during the first two of operations related to frequency drifts of the Magnetron transmitter After above repair and redesign of the IF filters, SELEX have demonstrated only a small residual effect on ZDR during the first hour of operation (still under investigation)

Analysis of strong clutter targets Returns from strong clutter targets confirms the ZDR drifts observed in light rain and its association with frequency drifts Also highlighted dBZ calibration jumps of ~1 dB affecting occasional scans on isolated occasions seem to be associated with the automated routine to measure background noise levels Only occurs on a couple of days Cause still under investigation…

Summary Overall dBZ/ZDR calibration corrections have been determined: -4.75 dB /-1.2dB Additional drift affecting ZDR in the first 2 hours of operation identified and associated with frequency changes. frequency changes were recorded and will be used to correct these effects Calibration corrections are to be applied to the entire data set in the next few months for overall offsets and ZDR drifts. A correction for dual-PRF velocity de-aliasing errors has been tested and will be implemented, improving the quality of Doppler velocity measurements Sporadic calibration jumps have been identified on a few occasions and are still to be investigated. Data from a few problem days may be withheld until the source of the calibration jumps has been determined.