EGPM

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EGPM

• The European Contribution to Global Precipitation
  Measurement

System Concept
C.C. Lin, M. Aguirre, U. Klein, B. Rommen, P.
Vogel ESTEC, Noordwijk, The Netherlands
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Artists View
Active/passive microwave sensing well established
Innovation imaging sounding radar
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Overall System Concept
4th Intl GPM Planning Meeting Greenbelt, 15-17
June 2004 EGPM
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EGPM Observation Requirements
(POD probability of detection, FAR false
alarm rate) Notes () this also includes e.g.
hail () this is liquid water equivalent ()
this requires a GPM constellation
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Orbit Selection

• Sun-synchronous orbit LTDN1430 is complementary
  to other GPM satellites
• NPOESS-1 (0930 des.)
• NPOESS-2 (1330 asc.)
• NPOESS-3 (0530 des.)
• Specified orbit range was 500-675 km, but 530-590
  km zone is unsuitable due to Earth resonance
• Phase A studies lead to orbit in 510-520 km range
• Coverage is function of the altitude

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Instrument Registration

• Conically scanning radiometer
• Nadir looking precipitation radar with three
  beams
• The 3 beams of the radar fill the central pixels
  of the reference 36 GHz radiometer channel

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Radiometer - I

• Five channels 18.7, 23.8, 36.5, 89 and 150 GHz
• Dual Polarization except for 23.8 GHz
• Two sounding bands 52.5 and 118.75 GHz, each one
  with 4 channels
• Antenna aperture ? 1 m for 510 km orbit altitude
• Rotation speed 31 rpm
• Radiometric sensitivity
• 0.5 K for lowest frequencies
• 1 K for 89 GHz and higher
• Footprint diameter at 36.5 GHz ? 13.5 km
• Instrument mass ? 130 kg Power ? 110 W Data
  rate ? 62 kb/s

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Radiometer - II
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Precipitation Radar

• 35.505 GHz
• Three switched beams
• Short pulse, EIK driven
• Sensitivity
• Integration Thres. Goal
• 4 km -0.7 dBZ 1.7 dBZ
• 20?13 km2 -7.7 dBZ -4.4 dBZ
• Vertical resolution 200 m
• Antenna diameter 1.3 m
• 4.3 km diameter footprint
• Instrument mass ? 55 kg Power ? 85 W Data rate
  ? 45 kb/s

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Satellite and Platform

• Earth pointed satellite with radiometer on zenith
  face and radar on anti-sun face
• Configuration drivers
• Need for radiometer fore and aft views
• Radar/Radiometer radio-frequency compatibility
• Drag reduction
• All sub-systems based on qualified technologies
• GaAs solar array fixed for drag minimization
• S and X (10Mb/s) band
• downlinks
• Centralized OBDH
• AOCS compensates the angular momentum of the
  radiometer. Unbalances and misalignments limited
  by manufacturing tolerances.

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Satellite Budgets and Launcher

• Satellite mass ? 800 kg
• Satellite power ? 600 W
• Satellite life of 3 years for the satellite (2
  additional years for consumables)
• Pointing accuracy (3?) is 2 mrad (3.5 required),
  co-registration is 1.55 mrad (2 required)
• 0.9 Gb per orbit, 3 Gb of memory
• Compact satellite
• Comfortable mass and adequate volume margins for
  launchers of the Rockot-Vega family

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Ground Segment
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Engineering Performance Radar - I
Radiometric performance at the top of the
precipitation layer for an along-track
integration distance of 4 km (single beam)
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Engineering Performance Radar - II
Radiometric performance at the top of the
precipitation layer for 20 km ? 13 km integration
(mission reference resolution)
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Engineering Performance Radiometer

• Performance figures obtained by standard
  modelling techniques
• Figures used as inputs to the end-to-end
  performance analysis
• All figures within requirements, but for NE?T
  (sensitivity) at 150 GHz
• Performance fulfills mission requirements

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System Concept Summary

• Compact satellite design with a maximum
  science-to-cost ratio (two very similar satellite
  designs)
• High sensitivity radiometer and radar, optimised
  for observation of high latitude precipitation
  (low rate and solid precipitation).
• Satellite design adaptable to different LTDN
• The ground segment concept supports the needs of
  the various types of users science and
  operational in NRT and RT, and interfaces with
  the GPM PPS (expected to further evolve under
  Earth Watch/GMES context)
• The phase A study teams under the leaderships of
  Astrium Ltd. and Carlo Gavazzi Space are
  acknowledged for their excellent design work