Download - CLP Measurement Technologies Passive Microwave

May 28, 2003 CLP Measurement – Passive Microwave

Goddard SpaceFlight Center

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CLP Measurement Technologies Passive Microwave

Passive Microwave Team at NASA Goddard Space Flight Center



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Outline

• Developed study strategy• Determined key driving parameters• Chose candidate orbit• Developed science performance metrics• Prioritizing study areas• Preliminary identification of technology drivers



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Cold Land Passive MW Concepts

• Real aperture– Dual frequency, dual polarization, conical scanning– 6-m deployable reflector, multiple feedhorns– Reflector emissivity and spin rate are concern

• 1-D STAR– Dual frequency, dual (or single) polarization– 6-m deployable cylindrical reflector– Nearly constant 50o incidence angle

• 2-D STAR– Single frequency, single polarization– Three 3-m deployable arms each with 250 elements– Multiple incidence angles (nadir to >50 degrees)



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25x25 km 5x5 km

Red = catchments with <100 pixelsat indicated spatial resolution



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Study Approach- Key Parameters

• Three strawman passive concepts were chosen by the CLPWG at the Ann Arbor Meeting (Nov 2002)

• Each is paired with a driving remote sensing science parameter, which directs our investigation

Concept Key RS science parameter

Key technology parameter

Real aperture Spatial resolution Aperture diameter

1D-STAR Spatial resolution Array size

2D-STAR NEDT Thinning/power



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Technology Development Issues for Real Aperture Concept

• Issues– Balance and Power Transfer Assembly (BAPTA)– Active system would be de-spun ( e.g. inside BAPTA)– Momentum compensation– Deployment / alignment , thermal stability

• Notes – “conventional“ concept– Largest rotating reflector system ever flown for MW instrument– Lifetime issues with mechanism, will drive spacecraft design



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Technology Development Issues for 1D-STAR Concept

65 elements/channel to get a reasonable NEDT (<1K)

• Issues– Stow and deploy fixed mesh reflector system– Material selection of mesh/coatings – Surface control of mesh backing structure– Reduce power required for multi-channel, multi-pol receivers– Lots of cabling & interconnects– Calibration

• Notes– Need deployment mechanism, but no spinning mechanism– Graceful degradation if/as receivers die– No technology heritage at high frequencies, spaceborne LRR might

demonstrate STAR at 19, 37.



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Technology Development Issues for 2D STAR Concept

~700 elements/channel gives 1.5K NEDT

• Issues– Stow and deploy boom structure– 2D STAR receivers at 19 and 37 GHz will need to be packaged

densely to minimize image aliasing– Current technology: rcvrs~0.5W/chan; 0.5-1.0 mW/correlation– Reduce Power required for multi-channel, multi-pol receivers– Interconnects and signal distribution– Calibration

• Notes – Single stage deployment, no moving parts after deployment– Power will be large, and interconnects are complex



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Summary & Next Tasks

• Spatial resolution– Aperture diameter

– Surface figure

– Mass

• Brightness temperature uncertainty– Emissivity

– Surface figure

– NEDT

– Thermal stability

• Swath width/coverage– Antenna geometry

– Beamwidth of STAR elements

– STAR bandwidth

• Compatibility with SAR• Interface characteristics

– ACS

– Power

– Thermal



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Technology Assessment

• Concentrate on 1-D STAR and real aperture– Most promising for fusion with SAR– Electrically the simplest vs. 2D, – Mechanically more complex vs. 2D

• Questions identified – How to integrate with SAR– Engineering issues: thermal, deployment/

packaging-in-shroud, power, mass, cabling/ inter-connects, reflector (solid, mesh, etc), metrology

• Answers lead to technology needs



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(show animation)

1D-STAR concept deployment



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Some Technologies Already Identified

• Mesh for reflector (1D-STAR and Real Aperture)– 14 / 19 / 37 GHz operation– Surface figure: ~200 um rms

• BAPTA for Real Aperture concept– Keep SAR feed static at focal point– Rotate radiometers with reflector



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Next tasks

– Examine SAR integration with 1D-STAR– Continue detailed study of Real Aperture– Assess state-of-the-art TRL– Tie technologies to science metrics– Determine break points in metrics where

technology development is needed– Make roadmaps