The A-Train: How Formation Flying Is Transforming Remote Sensing

Stanley Q. KidderJ. Adam Kankiewicz

andThomas H. Vonder Haar

Cooperative Institute for Research in the Atmosphere

(CIRA)Colorado State University

2

The A-Train

Aura

PARASOLCloudSatCALIPSO Aqua

13:3013:3113:31:13

13:32:11

13:45

MODISAIRSAMSR-EAMSUHSBCERES

CPRCALIOPIIRWFCPOLDER

HIRDLSTESMLSOMI

3

Formation Flying:Control Boxes

Aura is maintained

~15 minutes (~6750 km) behind Aqua

58 sec435 km

73 sec547 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

Formation Flying: Horizontal Separation

Equator

20°N

40°N

40°S

20°S

60°W 30°W 0°

CloudSat

CALIPSO

Aqua

PARASOL

Aura

5

Formation Flying:Horizontal Separation

NIGHT

DAY

Aqua

CloudSat & CALIPSO215 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

Formation Flying:Footprint Overlap

Courtesy of Ron Boain/JPL

Time-adjustedLidar footprint

Actual: Footprints overlap more than 90% of the time

Goal: Footprints overlap 50% of the time

Lidar footprint

Radar footprint

MotionLidar footprint(Diameter = 70 m)

Radar footprint

(Diameter = 1400 m)

2000 m

15 seconds(

113 km)Motion

Requirement: Footprints within 2 km

Time-adjustedLidar footprint

7

Mid-Level Clouds

Altocumulus / Altostratus

Cirrus

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

B

A

Mixed-Phase Clouds Viewed By MODIS

7/21/06 22:55 UTCMODIS 11 µm

−166− 168− 170− 172− 174− 176− 178

− 22

− 24

− 26

− 28

10

VIIRS Cloud Phase

Algorithm B

A

Mixed-Phase Clouds Viewed By MODIS

11

CloudSat Radar Reflectivity (dBZ)

CloudSat Radar Reflectivity (dBZ)

B (south)A (north)

Hei

gh

t (k

m)

0

5

10

Hei

gh

t (k

m)

0

5

10 CALIPSO 532 nm Backscatter

-40

-30

-20

-10

0

CloudSat & CALIPSO Data

12

Hei

gh

t (k

m)

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 Centerhttp://cloudsat.cira.colostate.edu

13

Hei

gh

t (k

m)

0

5

10

25

-35

TB

11 (

°C)

MODIS TB11

With MODIS Data

A (north) B (south)

CloudSat Data Processing Centerhttp://cloudsat.cira.colostate.edu

14

Hei

gh

t (k

m)

0

5

10

25

-35

TB

11 (

°C)

With VIIRS Cloud Phase

A (north) B (south)

CloudSat Data Processing Centerhttp://cloudsat.cira.colostate.edu

15

The Future: More satellites

Joining the A-Train in 2008 or 2009 are GLORY and OCO

16

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

LANDSAT 7EO-1

SAC C TERRA

Orbital Plane

Equator

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

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

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, andThere aren’t enough letters in the alphabet to name all of the “trains” which will soon be flying.