Mission: Racetrack Central
Priority: High
 
This mission is designed to fly three circuits of a “racetrack” pattern along a low-latency ICESat-2 ground track. The two legs of the racetrack are the “D” and “F” (strong TEP beams) of the selected RGT. The three circuits are designed to widen the composite swath of each leg, to improve the changes of coincident OIB and ICESat-2 measurements in the presence of ice drift.
 
Moderate katabatic flow in the Holmes Glacier catchment, and the position of this offshore line between two Southern Ocean low pressure systems, made this mission a viable option today. We observed completely clear skies on the entire survey line. The southern 25% of the survey pattern appeared to be over shore-fast ice, the rest over mobile pack ice.  We flew the line at 3400 ft AGL, as requested by the OIB science team and away from the snow radar’s Nyquist AGL zones. ECMWF and GFS forecast models led us to expect a light westerly crosswind component of about 6 kt on-station. Because we expected to be well-established on the RGT centerline when ICESat-2 passed overhead, we elected not to offset the lines for the westerly wind. We encountered an unusually strong headwind (up to 75 kt) on the transit from Hobart to the survey, which delayed our arrival on-station by ~30 min, but we still managed to get established on the line 2 min prior to ICESat-2 passing overhead at 00:05:54 UTC. Measured winds on-site, from the aircraft's air data computer, showed that the actual winds, and thus the approximate ice drift, were more closely aligned with our flight track (within 20º at all times) than we expected from the models, though still usually with a slight westerly component. All instruments performed well, with 100% successful data collection during nearly 3 h of survey time. We performed a ramp pass at 1500 ft AGL on arrival at Hobart.
 
ICESat-2 RGT / latency (± indicates OIB surveyed after/before ICESat-2)
0673 / zero latency, overpass at 00:05:54 UTC
 
Attached images

1. Map of today’s mission (John Sonntag / NASA)
2. KML of today’s mission (John Sonntag / NASA)
3. Today's planned flightline (black) overlaid on a recent AMSR-2 sea ice concentration image, with Antarctica in red, and open water in magenta; we use this product on a regular basis to fine-tune our sea ice flight plans (AMSR-2 product courtesy University of Bremen)
4. A wide lead, running roughly parallel to the Antarctic coastline, which separated shore-fast sea ice at right from the mobile ice pack at left (John Sonntag / NASA)
5. Texture of sea ice near the north end of today's lines (John Sonntag / NASA).
6. Screen capture of ATM's "SOXMap" navigation display, as we entered our sixth and final survey line, illustrating how today's elongated "racetrack" pattern combines six separate ATM T-6 swaths (in green) to form two much wider composite swaths, centered on ICESat-2 RGT 0673 beams 2R and 3R (NASA ATM team).