2007 Atlantic Hurricane Season 100 % of Storm Center Hit by ASCAT Swaths 90 % of Storm Center Hit by QuikScat Swaths 80 70 [%] 60 50 40 30 20 10 0 ET Andrea ET Chantal TS Erin TS Gabrielle TS Ingrid TS Jerry HU Lorenzo TD Fifteen Overall (5/8-5/14) (7/31-8/05) (8/13-8/18) (9/8-9/11) (9/12-9/18) (9/23-9/24) (9/25-9/29) (10/10-10/12) ET Barry HU Dean HU Felix HU Humberto TD Ten HU Karen TS Melissa HU Noel (5/31-8/5) (8/13-8/23) (8/28-9/5) (9/12-9/13) (9/21-9/22) (9/23-9/29) (9/28-10/5) (10/28-11/02) (a) 2007 Eastern Pacific Hurricane Season 100 90 % of Storm Center Hit by ASCAT Swaths % of Storm Center Hit by QuikScat Swaths 80 70 [%] 60 50 40 30 20 10 0 TS Five-E TS Dalila HU Flossie HU Henriette TD Thirteen-E TS Kiko TS Alvin TD Three-E (5/27-5/6) (5/11-5/15) (7/14-7/15) (7/22-7/30) (8/3-8/13) (8/30-9/5) (9/20-9/25) (10/15-10/27) HU Ivo TS Juliette TS Barbara TD Four-E HU Cosmo TS Erick TS Gil (5/29-6/2) (7/9-7/11) (7/14-7/24) (7/31-8/2) (8/29-9/3) (9/16-9/24) (9/29-10/5) Overall (b) fIGure 1. Percentage of time the center of named storms was observed with either QuikScat (blue) or ASCAT (orange) polar-orbiting scat- terometers during the 2007 Atlantic (a) and Pacific (b) hurricane season. Poor performance results from the coverage gaps and infrequent revisit times that are characteristic of polar-orbiting wide-swath imagers. passes through an imager's coverage gap or when its motion is appropriately offset from the motion of the imager's swath. The figure highlights the many cases in which TCs are resolved much less than half the time. One particularly egregious case is Hurricane Dean, which was sampled less than 5% of the time possible by ASCAT. JUNE 2013 ieee Geoscience and remote sensing magazine 2.3. MeasureMenT MeThodology Figure 2 illustrates the propagation and scattering geometries associated with the GNSS approach to ocean surface scatterometry. The direct GPS signal provides a coherent reference for the coded GPS transmit signal. It is received by an RHCP receive antenna on the zenith side of the spacecraft. The quasi-specular forward scattered signal from the ocean 53