1. The A-Train: How Formation Flying Is Transforming Remote Sensing Stanley Q. Kidder J. Adam Kankiewicz and Thomas H. Vonder Haar Cooperative Institute for Research in the Atmosphere (CIRA) Colorado State University

2. 2 The A-Train Aura PARASOL CloudSat CALIPSO Aqua 13:30 13:31 13:31:13 13:32:11 13:45 MODIS AIRS AMSR-E AMSU HSB CERES CPR CALIOP IIR WFC POLDER HIRDLS TES MLS OMI

3. 3 Formation Flying: Control Boxes Aura is maintained ~15 minutes (~6750 km) behind Aqua 58 sec 435 km 73 sec 547 km Aqua, CALIPSO, and PARASOL are maintained in control boxes of ±21.5 seconds (±158 km) AquaCALIPSOPARASOL CloudSat is maintained 12.5 ± 2.5 seconds ahead of CALIPSO

4. 4 Formation Flying: Horizontal Separation Equator 20°N 40°N 40°S 20°S 60°W30°W0° CloudSat CALIPSO Aqua PARASOL Aura

5. 5 Formation Flying: Horizontal Separation NIGHT DAY Aqua CloudSat & CALIPSO 215 km Ascending Node Descending Node To avoid sun glint, CALIPSO and CloudSat are offset 215 km in the anti- solar direction (maximum 240 km) from Aqua’s ground track at the ascending node.

6. 6 Formation Flying: Footprint Overlap Courtesy of Ron Boain/JPL Time-adjusted Lidar footprint Actual: Footprints overlap more than 90% of the time Goal: Footprints overlap 50% of the time Lidar footprint Radar footprint Motion Lidar footprint (Diameter = 70 m) Radar footprint (Diameter = 1400 m) 2000 m 15 seconds (  113 km) Motion Requirement: Footprints within 2 km Time-adjusted Lidar footprint

7. 7 Mid-Level Clouds Altocumulus / Altostratus Cirrus

8. 8 Cloud Layer Experiments (CLEX) Ten experiments since 1995 Generating Cells ~ 1-1.5 km in Length What we have learned: Ice Below Typical Particle Concentrations: 100-200 cm -3 (Liquid) 20-150 L -1 (Ice) Liquid Water on Top Aircraft Measurements Precipitating Ice Region (~.2-2.5 km deep) Optically Opaque Mixed-Phase Region (~300-500 m deep)

9. 9 B A Mixed-Phase Clouds Viewed By MODIS 7/21/06 22:55 UTC MODIS 11 µm −166− 168− 170− 172− 174− 176− 178 − 22 − 24 − 26 − 28

10. 10 VIIRS Cloud Phase Algorithm B A Mixed-Phase Clouds Viewed By MODIS

11. 11 CloudSat Radar Reflectivity (dBZ) B (south) A (north) Height (km) 0 5 10 Height (km) 0 5 10 CALIPSO 532 nm Backscatter -40 -30 -20 -10 0 CloudSat & CALIPSO Data

12. 12 Height (km) 0 5 10 GEOPROF-Lidar Cloud Layers: Detected by CloudSat Detected by CALIPSO MODIS TB11 Combined CloudSat & CALIPSO Data A (north)B (south) CloudSat Data Processing Center http://cloudsat.cira.colostate.edu

13. 13 Height (km) 0 5 10 25 -35 TB11 (°C) MODIS TB11 With MODIS Data A (north)B (south) CloudSat Data Processing Center http://cloudsat.cira.colostate.edu

14. 14 Height (km) 0 5 10 25 -35 TB11 (°C) With VIIRS Cloud Phase A (north)B (south) CloudSat Data Processing Center http://cloudsat.cira.colostate.edu

15. 15 The Future: More satellites Joining the A-Train in 2008 or 2009 are GLORY and OCO

16. 16 The Future: More Trains The A-Train was not the first Train: EO-1 flew 1 min behind Landsat 7 SAC-C flew 27 min behind EO-1 Terra flew 2.5 min behind SAC-C

17. 17 The Future: Overflyers A-Train (705 km) NPP (~824 km) Satellites in the same orbital plane, but at different altitudes would leverage the extensive cal/val efforts of the A-Train satellites (or satellites in other trains).

18. 18 Conclusions The A-Train has definitively proven the concept of Formation Flying, The synergy of nearly coincident observations from multiple instruments has transformed remote sensing of the atmosphere, and There aren’t enough letters in the alphabet to name all of the “trains” which will soon be flying.