CYGNSS Mission Overview and Level 1 DDM Calibration - E-GEM

CYGNSS Mission Overview
and
Level 1 DDM Calibration
Chris Ruf
E‐GEM Workshop, Quebec City, 19 July 2014
Outline
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Mission Overview
Observatory Hardware
Constellation Deployment and Dispersion
Spatial and Temporal Sampling
Level 1 Calibration of Delay‐Doppler Maps
Schedule
Ruf, CYGNSS, E‐GEM Wkshp 19 Jul 2014
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CYGNSS Mission Overview
• The Cyclone Global Navigation Satellite System (CYGNSS) is the NASA Earth Venture Mission selected in June 2012
• The driving science objective is rapid sampling of ocean surface winds in the inner core of tropical cyclones
• CYGNSS Mission Design
– Eight small satellites in low earth orbit at 35o inclination, each carrying radar receivers capable of four simultaneous bi‐static scatterometer measurements of GPS signals scattered from the ocean surface
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CYGNSS Observatory
and Key Components
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CYGNSS Flight Segment Characteristics
8 Observatories
– Size and shape driven by 2 nadir science ant and 100% science duty cycle
– Mass: 25.5kg (each)
– Power: 34.4W avg load
– Attitude control: 3‐axis nadir
– Comm: 4Mbps S‐band
Launch Vehicle and Deployment Module
– Single LV, GFE
– Altitude: 500km
– Inclination: 35deg
– LV: Pegasus
– Launch: Oct 2016
– Operations: 2+ years
Volume
– 51x59x24cm (stowed)
– 51x159x24cm (deployed)
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Day 27 after deployment
Spatial Coverage in 24 hr Period
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CYGNSS Spatial Sampling
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CYGNSS Temporal Sampling
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Temporal sampling is not
deterministic due to
asynchronous CYGNSS and
GPS orbits
Model revisit time as a
random variable with
empirical probability
density function (PDF)
derived from Monte Carlo
simulations
Revisit time PDF shown at
right
Median revisit time = 2.8 hr
Mean revisit time = 5.9 hr
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End‐to‐End Simulator Example of CYGNSS Spatial and Temporal Coverage
13-day Nature Run Storm Center Track
Nolan, D. S., R. Atlas, K. T. Bhatia, and L. R. Bucci, 2013: Development and validation of a hurricane nature run using the Joint OSSE Nature Run and the WRF model. J. Adv. Earth. Model. Syst., 5 , 1‐24.
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CYGNSS Sampling of Nature Run
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Level 1 Calibration of DDMs
(Scott Gleason, CYGNSS Instrument Scientist)
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Data Level Definitions
• Level 0, Raw DDMs telemetered to ground
• Level 1, Calibrated DDMs
– L1A, DDM received power in each delay,Doppler bin (watts) – L1B, DDM bi‐static scattering cross section,  in each
delay,Doppler bin m2)
• Level 2, Geophysical products in instrument sampling time,space coordinates
– Ocean surface wind speed, 25 km averaged, 10 m referenced (Clarizia)
– Mean squared slope, 25 km averaged (Zavorotny)
• Level 3, various re‐gridded, variable spatial res, inputs other than L1B product, … (Atlas, Majumdar, Garrison, Katzberg, Johnson, …)
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Level 1a Calibration
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Convert Raw DDM (in counts) to Received Power DDM (in Watts)
Compressed Science DDM’s consist of smaller area (5 KHz x 4 chips, 11 x 17 samples) near the specular reflection point
DDM in Watts (Level 1a)
DDM in Counts (Level 0)
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Open Ocean DDM
L1a Algorithm
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Routine 1Hz L1a signal power DDM (in Watts) can be expressed as,
Level 0 DDM
Noise Floor
Black Body DDM
Black Body Power
Instrument Noise
Power
Black Body Counts
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CN estimated from each DDM, at delays where no signal is present
Pr is estimated using temperature‐
dependent LUT, updated using Open Ocean calibration
PB and CB estimated from Black Body noise‐only DDM
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Noise
Samples
128
Delay
Samples
20 Doppler Bins
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Level 1b Calibration
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Convert L1a DDMs (in Watts) to DDMs in units of bi‐static scattering cross section by unwrapping the radar range equation [e.g. Zavorotny and Voronovich, 2000]
2 (Level 1b)
DDM in meter
DDM in Watts
DDM in Watts (Level 1a)
DDM in Counts
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Expression for L1b Product
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Obtained by solving the L1a signal power equation for the effective bistatic cross section
Ranges
L1a
GPS Tx
Power
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GPS Tx Rx
Gain Gain
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From L1a to L1b Observables
The plot shows L1a
and L1b DDMA for a
Range Corrected Gain
(RCG) > 20*10-27
GRX
RCG  2 2
RTX RRX
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Level 1 Cal/Val with
Ground Based Beacon
• Beacon transmits a modulated L1 signal from the ground to a CYGNSS observatory
• Transmit signal is phase‐
locked to direct GPS signal overhead
• The Beacon will be used to verify the DDMI’s:
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Signal power measurement
Antenna pattern
Prediction of location
Noise measurement/Noise figure
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Project Schedule
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