solid-state weather radar pulse compression receiver and...
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MS Final Exam
Frequency Diversity Wideband Digital Receiver And Signal Processor For Solid-State Dual-Polarimetric Weather Radars
Kumar Vijay Mishra
Advisor: Dr V. Chandrasekar
Committee: Dr A. Jayasumana and Dr P. Mielke Jr.
June 15, 2012
Background Photograph by
Kumar Vijay Mishra
MS Final Exam
Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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MS Final Exam
• Weather radar equation (Probert-Jones, 1962)
• Radar observables in terms of backscattering matrix
Duplexer
Duplexer
To H-receiver
To V-receiver
h- port
v- port
H-Transmitter
V-Transmitter
STALO/
COHO
Range R
Δ r = cτ/2
Tx - H
Tx - V
Rx - H
Rx - V Shh Shv
Svv Svh
Shh Shv
Svv Svh
Sinclair Matrix
Signal Theory of Weather Radars
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MS Final Exam
Context of Solid-state transmitters for weather radars • WWII: Weather echoes identified as clutter on military radars (Atlas et. al., 1990)
• 1950s: Application of backscatter matrix in radar (Kennaugh, Ohio State)
• 1975 (Ulbrich et. al.): Backscatter matrix application to meteorological radars
• 1976 (Seliga and Bringi): Polarization diversity in weather radars
• 1979 (Seliga et. al.): First measurement of Zdr with CHILL
• Early-to-mid 1990s (Klazura et. al.): Ground-based scanning weather radar
network (WSR-88D)
• Mid-1990s (Ackerman and Stokes): ARM program for vertically-pointing radars
• 1996: First weather radar digital IF receiver introduced by Vaisala
• 1997 (Kummerow): First spaceborne weather radar (TRMM)
• Early 2000s: X-band weather radar networks (CASA IP1)
• Late 2000s: Solid-state transmitters for weather radars (HIWRAP, WiBEX, D3R)
• Low operating power, high duty cycle, higher reliability, extremely wide
bandwidth, digital control, longer operating life
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MS Final Exam
Aspects of solid-state transmitter weather radars
• The intensity of the weather is determined by measuring the
reflectivity of the volume of precipitation particles.
• Reflectivity is measured from the received signal at the antenna
reference port:
• min(Ze) is a function of transmit pulse width for a given
transmitter and antenna.
• Long transmit pulses (= degraded range resolution) are required
for adequate sensitivity in low-power solid-state transmitters.
[Bringi and Chandrasekar, 2002]
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MS Final Exam
Aspects of solid-state transmitter weather radars (contd.)
• Pulse Compression waveforms can enable solid-state transmitter
technology
• Improves range resolution and reduces peak-power requirement
• Increases sensitivity
• Improves accuracy of estimates through range averaging
• Increases dynamic range beyond RF hardware limitations
• Common usage in hard target radars (Lewis et. al., 1986) and lidars
(Oliver, 1979)
• Use in weather radars has been limited
• Range sidelobes degrade measurements for volume targets
• Introduces blind zones in the measurements
• Implications of wider bandwidth (Yoshikawa, 2010)
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MS Final Exam
Aspects of solid-state transmitter weather radars (contd.)
• Frequency diversity waveforms
• Multiple subpulses transmitted to
avoid blind zones (Bharadwaj et.
al., 2009)
• Low ISL pulse compression filters
employed
• Multi-channel wideband digital
receivers
• Potential deployment of
waveforms
• D3R (Operational) (Chandrasekar
et. al., 2010)
• WiBEX (Under development)
(George et. al., 2010)
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MS Final Exam
Existing Weather Radar Digital IF Receivers Context of a generic digital receiver in a radar system
Commercial Solutions: Vaisala RVP Series (NEXRAD, TDWR), GAMIC
ENIGMA series (DWD, Radtec), Gematronik GDRX series (Australian and Dutch weather radar network).
Research Solutions: CSU-CHILL Digital Receiver (George, 2007), CASA
EDAQ Series (Khasgiwale, 2005), USRP-II (Vierinen et. al., 2009)
Multi-pulse frequency diversity processing is currently not available on these receivers
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Common Features of Weather Radar Digital IF Receivers
• Operational Requirements
• Polarization agility
• Polarization diversity
• On-board transmit control
• Calibration, Test and
Debugging
• Transmit pulse sampling
• BIST and BITE
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• Performance Requirements
• Wide dynamic range
• Dual PRF and Staggered PRT
processing
• Multi-trip echo recovery
• Pulse compression
• Clutter filtering
• Attenuation correction
MS Final Exam
Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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MS Final Exam
Wideband Digital IF Receiver Hardware • Hardware
• Pentek 7150 board with Quad 200MHz 16-bit TI ADS5485 ADCs with Virtex - 5 SX95T as processing FPGA
• Software
• Pentek libraries (ReadyFlow) for PCI-based communication
• Standard FPGA development software (ModelSim, ISE, ChipscopePro)
• Function
• Analog to digital conversion of IF signal
• Digital downconversion
• Digital pulse compression
• Framing, antenna position decoding, IRIG-B decoding
PMC P4 Interface
26-Pin LVPECL Front Panel SMC Connectors
for signal and clock inputs
PCI Interface
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Digital Receiver Board • Development environment
• PMC mounted on Technobox 4733 PMC adapter and 4936 Fan assembly
• Field deployment
• Single board computer and cPCI carrier board with a PMC slot (Concurrent Technologies)
7150 PMC 4733 PMC Adapter
4936 Fan Assembly
7150 PMC mounted on the chassis of a lab computer
PMC DRX card mounted on a single-board computer
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Block Diagram of DRX Hardware
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MS Final Exam
DRX Hardware Features • Processing FPGA
• The digitized data from ADCs is sampled and processed
• Available for user to configure
• Interface FPGA
• Board interfaces (PCI-X, PCIe)
• Not accessible to the user
• Onboard clock and timing circuits
• Four ADCs, DDR2 SDRAM
• Voltage and temperature sensors
• LVPECL, LVDS, SMC, Custom I/O interfaces available
• Separate connectors for external clock and PPS signals
Sample output for a successful sensor data query
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Principle of Operation and Interfaces • PMC Baseboard Interface
• SBC communication and LVDS Connections
• SMC inputs for RF signals, clock and PPS
• FPGA interfaces
• Online configuration through Interface FPGA
• JTAG assembly interface for debugging
• DMA Interrupts, temperature and voltage sensors
• Waveform generator (George et. al., 2010)
• System triggers through SCSI
• Modbus programming
• Antenna position interface
• GPS timestamp interface 15/61
MS Final Exam
Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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Digital Receiver FPGA Design Requirements • Total number of channels = 12 (Two polarizations for three subpulses
downconverted to I and Q)
• Cost of filter chain for all twelve channels is expensive in terms of logic
and multipliers
• Other Requirements/Features
• Process all range gates for each channel (including transmit pulse
sample)
• Programmable Built-In Self Test (BIST) option
• Online digital health report
• Option of data available without pulse compression
• Several configurable features and scalability
• Programmable sampling (1MHz to 10 MHz)
• Multiple DMA data transfer logic
• Simultaneously archive time-series for all 12 channels on RAID
• Interface with Positioner and GPS decoder software 17/61
MS Final Exam
Design Philosophy • Xilinx Virtex-5 SX95T FPGA
• SXT family is rich in signal processing resources
• 14720 Logic Slices, 640 DSP48Es, 6 CMTs, ~10 Mb RAM, fmax = 550 MHz
• IF Subsampling required (Narrowband interpretation of Nyquist criterion)
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Three-pulse waveform at IF=140MHz Inverted image
of the signal at 60 MHz
MS Final Exam
Design Philosophy (contd.) • Virtex SXT95 FPGA
• Pentek’s own design occupies 50% of the logic
• Design Challenge
• Cost of filter chain: MATLAB Implementation of one subpulse channel
• SX95T has only 640 DSP48Es: resource savvy FPGA design is required.
Filter Taps Mults
(MATLAB)
Halfband Filter 1 23 13
Halfband Filter 2 23 13
Decimation Filter 255 205
Cascade of
Decimation Filters (=
1+2+3)
301 231
40 µs Pulse
Compression Filter
400 401
20 µs Pulse
Compression Filter
200 201
Total 833 (130%)
DSP48Es
(FPGA)
4
4
13
21
22
12
55 (8%)
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D3R Multichannel Pulse Compression Digital Receiver
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An illustration of the design
MS Final Exam
Direct Digital Synthesis and Quadrature Modulation
• Combination of single- and dual-channel implementation
• SFDR: 105 dB.
• Phase-dithered noise shaping for multi-carrier implementation
• Programmable DDS frequencies
MATLAB Fixed-Point Simulation
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HDL Implementation
MS Final Exam
Decimation and Filtering Chain • Halfband filters perform decimation
without decreasing the dynamic range
of digitized signal
• A combination of halfband filters and
polyphase decimator is used here
• Better filtering response compared to
CIC-FIR compensator filters
• Halfband filters save on logic compared
to traditional CIC filters
• Halfband filters configured as
polyphase filters enabling further
reduction in multipliers
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Digital Pulse Compression • Single-rate multi-channel FIR filters
• Complex filter implemented as two real filters
• Asymmetric and reloadable coefficients
• Multicolumn support possible by increasing the clock
rate
• DPC performance between filtered and ideal case ~1 dB
Chirp Bandwidth = 8 MHz
f1 (40 µs)
At = 0.3543
Ab = 0.6
α = 0.1268
PSL (dB) Filtered -67.1131
Ideal -68.4130
ISL (dB) Filtered -71.2546
Ideal -71.0741
f2 (20 µs)
At = 0.3274
Ab = 0.4920
α = 0.1944
PSL (dB) Filtered -64.0029
Ideal -66.1038
ISL (dB) Filtered -66.6472
Ideal -67.5288
Fixed-point implementation of the filter chain (Lp-norm Version 1 waveform)
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04/27/2010
Comparison of DPC in ADC vs BIST mode
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Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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MS Final Exam
• Raw I-Q time series data of
digital receiver is processed
by Intel Xeon Octal-Core
processors operating on
Linux
• Communication over
Gigabit Ethernet link
• Remote operation and
control of processing nodes
possible
• All range profiles of all
subpulses are archived and
available for processing
• Scalable design
Signal Processor Architecture
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MS Final Exam
Time Series Acquisition And Dissemination Server
Network Socket
Receive Thread
Circular
Buffer
Socket
Client
Thread
Socket
Client
Thread
Time Series
Archiver
Server
Moment
Server
DRX Single
board
Computer
Gig
abit
Eth
ern
et
• Acquires raw time series data from DRX SBC in real-time
• Streams data back to multiple clients
• Ideal to handle massive data volume if the bandwidth of the link is
limited (such as a link over the slip rings)
Time Series Acquisition And Dissemination Server
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Moment Server
• Computes meteorological
products from the raw
time series data
• I-Q Processing using
GNU Scientific Library
(GSL)
• Separate threads to
compute moments for all
range gates of three
subpulses
• Single range profile is
then generated by
merging the moments
• Product data is made
available to multiple
clients 28/61
MS Final Exam
Time Series Archiver Server
Network Socket
Receive Thread
Circular
Buffer
Disk Write
Thread
Time Series
Acquisition
Server
Gig
abit
Eth
ern
et
RAID
Time
Stamp
Files
Replay Server
Disk Read
Thread
Replay Client
Thread
Circular
Buffer
Moment
Server
• Time series data is archived for all range gates for all subpulses
• The sampled transmit pulse data is also included in the archive
• The replay server can be used to read back the time series data and
stream it to the moment server
Time Series Archiver And Replay Server
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Calibration Mode • The product profiles are not merged
• Any subpulse profile is individually available
• Integration can be varied from 8 to 2048 samples
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Staggered PRT Mode • Signal Processor choses algorithm for mean-velocity and spectrum width
based on the time series flags
• Velocity Spectrum Width
• Staggered PRT LDR Processing Mode
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SES Processing Mode
• Sensitivity Enhanced System
(SES) uses medium pulse
echoes to process long pulse
echo to enhance the sensitivity
of the system (Chandrasekar
and Nguyen, 2010)
• Long pulse is designed with
larger native range resolution
and less receiver noise
• DPC module of the DRX is
configured to act as a serial
delay block
• Passband of the long pulse
decimation filter is narrower
• Short pulse is eliminated
DRX SES Performance for a light rain event on Sept 15, 2011 Nguyen et.al., "Sensitivity enhancement system for pulse compression weather
radar", 35th AMS Conference on Radar Meteorology, 2011
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MS Final Exam
Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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MS Final Exam
NASA Dual-Frequency Dual-Polarized Doppler Radar
• Ground Validation radar for Global
Precipitation Mission [Chandrasekar et. al.,
2010]
• Waveform design challenges
• Sensitivity: -10 dBZ at 15 km to enable
snow measurements
• Maximum unambiguous range =30 km
• Precipitation measurements at highly
attenuating frequencies (Ku-band:
13.91±.25GHz, Ka-band: 35.56±.25GHz)
• Dual linear polarizations with both
simultaneous and alternate transmission
• Maximum unambiguous Doppler = 25 m/s
• Ground clutter suppression for non-uniform
sampling
• Ideal for deployment of multi-channel
digital receiver
D3R deployed at ARM Southern Great Plains
site during GPM Midlatitude Continental
Convective Clouds Experiment (MC3E)
(05/28/2011)
Photograph by: Kumar Vijay Mishra
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MS Final Exam
• D3R is jointly developed by Colorado
State University, NASA Goddard Space
Flight Center, Remote Sensing Solutions
• Antennas: Seavey Division of ARA, Inc.
• Pedestal: Orbital Systems
• Transceivers: RSS, Inc.
• Waveform Generator (CSU) (George et.
al., 2010)
• Display: GTK Display (CSU-CHILL)
• Currently uses a placeholder Ka transmitter
of 1 W peak power output
System Architecture
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Antenna and Pedestal
• First generation has beam-
aligned antennas on
common pedestal
• Single-aperture antenna
under development D3R Pedestal by Orbital
Systems
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Antenna Performance
• Gain = 44.5 dB
• HPBW ≤ 1°
• Copolar mismatch ≤ 5%
• ICPR2 ≥ 32 dB
• PSL ≥ 25 dB
Patterns data courtesy: GSFC/Seavey
Analysis by: Kumar Vijay Mishra
Ku Copolar Pattern Ku Sidelobe Envelope Ku Wide Angle Plot
Ku Crosspolar patterns Ka Crosspolar patterns 37/61
MS Final Exam
RF Front End
• Two-stage IF module (details omitted)
• Calibration Channel for sampling transmit pulse 38/61
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Digital Receivers
• DRX for Ku and Ka are identical systems
• Separate link for both SBCs over the slip ring
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Signal Processor and Display
• Moment servers are replicated for both
frequencies
• Separate displays for Ku and Ka
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D3R Waveform Design • The requirement for min(Ze)
directly maps to the pulse widths and number of subpulses
• Requirement of min(Ze) = -10 dBZ at 15 km is met at 150 m resolution
• The velocity requirement of 25 m/s is met with staggered PRT 2/3 scheme.
• Simultaneous mode: 400/610 us. Alternate mode: 500 us.
• Equivalent PRF = 5 kHz gives unambiguous Doppler of ~27 m/s
• Time-domain clutter suppression for non-uniform sampling [Nguyen et. al., 2009].
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Waveform Design: Chirp Bandwidth, Phase noise and Doppler
Sensitivity <- Ku Ka ->
ISL as function of Chirp Bandwidth
MS Final Exam
Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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Pulse Compression Filter Performance on Sampled Transmit Pulse (Jan 03 2012, D3R deployment at CSU-CHILL)
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Profile comparison across subpulses
• Data from D3R deployment during
MC3E campaign (May 31 2011)
• Reflectivity profiles are aligned after
range calibration
• 150 m range resolution
• The three subpulses demonstrate the
expected sensitivity: long pulse has
the highest sensitivity followed by
medium and short pulses.
• Medium and short pulses are matched
starting 3 km (blind range for medium
pulse)
• Long pulse is matched after the
corresponding blind range (= 9 km).
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Comparison across full range (MC3E data)
Comparison in high SNR regions
(deployment at CHILL site)
MS Final Exam
First Observations of Standard Moments: Merged profiles from three subpulses
• Data from D3R deployment during
MC3E campaign (May 31 2011)
• Data thresholded for low SNR values
• Standard pulse-pair estimates
• Staggered PRT mode: unfolded
velocity estimates shown
• Noise subtraction applied on the data
• Merged standard moments match
between subpulses.
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(Chandrasekar et. al., "Characterization of NASA Ku-Ka Band Dual-Frequency Dual-
Polarized Doppler Radar (D3R)", Precipitation Measurement Missions (PMM) Science
Team Meeting, 2010)
MS Final Exam
Staggered 2/3 PRT velocity estimates
04/27/2010
Simultaneous observations of D3R and CHILL during a rain event (Nov 1, 2011) 47/61
(Chandrasekar et. al., "Characterization of NASA Ku-Ka Band Dual-Frequency Dual-Polarized Doppler Radar (D3R)", Precipitation Measurement Missions (PMM) Science Team Meeting, 2010)
MS Final Exam
Comparison of Dual-Polarimetric Variables
04/27/2010
Simultaneous observations of D3R and CHILL
during an intense storm (July 10, 2011) 48/61
(Chandrasekar et. al., "Characterization of NASA Ku-Ka Band Dual-Frequency Dual-Polarized Doppler Radar (D3R)", Precipitation Measurement Missions (PMM) Science Team Meeting, 2010)
MS Final Exam
Observations during sphere calibration experiment
04/27/2010
Top: Near (13.9 km) range observation on D3R real-time display during
sphere calibration experiment at CSU-CHILL radar site on Sept 23,
2011. Bottom: The same observation at the far range (31.4 km). 49/61
MS Final Exam
Deployment at GCPEx Campaign
• D3R deployed at Environment
Canada (EC) Center for
Atmospheric Research
Experiments (CARE) site in
Egbert, Ontario to participate in
GCPEx
• The radar operated
uninterrupted from Jan 17, 2012
to Mar 1, 2012.
• Diverse meteorological events
observed by D3R (lake effect
snow, freezing rain, freezing
drizzle, light rain, light snow
flurries, heavy synoptic snow
etc.)
• New waveform with revised
calibration used
D3R deployed at Environment Canada site in
Egbert, Canada during GPM Cold Season
Precipitation Experiment (GCPEx) (01/14/2012)
Photograph by: Kumar Vijay Mishra
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D3R WKR WKR D3R
Zh
V
Example data from GCPEx campaign: Comparison between D3R and C-band WKR radar (Jan 17, 2012)
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Observations", IGARSS, 2012)
MS Final Exam
RHIs (Skydive Az = 87.8 deg) Passing rain-band and weakening melting layer
Jan 23 2012 Zh: 1437 UTC Zh: 1447 UTC
Zh: 1457 UTC Zh: 1507 UTC Zh: 1517 UTC Zh: 1526 UTC
• Melting layer at ~2.2 kms.
• Melting layer weakens in subsequent scans as the rain band crosses the sector.
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Cold rain observation on Ku and Ka RHIs (Skydive Az = 87.8 deg)
Jan 26, 2012
Ku Zh
0202 UTC
Ka Zh
0225 UTC 0244 UTC 0307 UTC 0329 UTC 0345 UTC
• Observation of mammatus clouds, brightband formation and freezing rain
• ~20 min snapshots from a set of RHI scans @ every 10 mins
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WKR Over-the-head RHIs
(Light snow event: 10 min snapshots)
D3R Ku Zh
WKR Reverse RHI
17:25:20-17:26:49
UTC
D3R Ku Zh
WKR RHI
17:27:04-17:28:29
UTC
D3R Ku Zh
WKR Reverse RHI
17:34:39-17:36:06
UTC
D3R Ku Zh
WKR RHI
17:36:16-17:37:45
UTC
D3R Ku Zh
WKR RHI
17:45:39-17:47:12
UTC
D3R Ku Zh
WKR Reverse RHI
17:43:54-17:45:28
UTC
Light snow echoes weaker than -5dBZ observed by Ku-band (Jan 28, 2012)
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Observations of an intense snow storm (Feb 29, 2012)
D3R Ku Zh
V
W
18:32 Z 19:32 Z 20:32 Z 21:32 Z
MS Final Exam
2012-02-29: Frequent Sampling of
Intense Snow Band
• 10 min snapshots of D3R RHI scans @ every 5 mins
• All RHIs: El = 1-60°
Ku Zh Mortons RHI
20:44 Z
Ku Zh KCR RHI
20:45 Z
Ku ρhv V-point
20:46 Z
Ku Zh Low El PPI
20:42 Z
Ku Zh Mortons RHI
20:54 Z
Ku Zh KCR RHI
20:53 Z
Ku ρhv V-point
20:55 Z
Ku Zh Low El PPI
20:52 Z 2042 Z 2052 Z
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Outline
• Introduction
• Context of Solid-State Transmitters in Weather Radars
• Existing Weather Radar Digital IF Receivers
• Digital Receiver solution for Solid-State Transmitter
Weather Radars
• Multi-Channel Receiver Design
• Processing Modes
• NASA D3R System
• First Results from Field Deployment
• Summary
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Summary
• A multi-channel digital receiver was designed, developed, tested
and deployed
• Implements an advanced frequency-diversity waveform
• Sidelobe performance is satisfactory for weather radars
• The data from the three pulses is merged seamlessly
• Real-time signal processor developed for the digital receiver
• Successful deployment in D3R radar
• Comparison with an S-band and C-band radar indicates the
products are correctly estimated
• Future work
• Phase-coding capability and alternate mode of transmission to be tested
• Real-time clutter suppression and attenuation correction algorithms to be
included in the signal processor 58/61
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Acknowledgments
Dr. V. Chandrasekar, Adviser
Dr. Anura Jayasumana, Committee Member
Dr. Paul Mielke Jr., Committee Member
Mathew Schwaller, Project Manager, NASA Goddard Space Flight Center
Patrick Kennedy , Facility Manager, CSU-CHILL
David Brunkow, Senior Engineer, CSU-CHILL
All former and current members of
CSU Radar and Communication Lab
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References
04/27/2010
• Kumar Vijay Mishra, V. Chandrasekar, Cuong Nguyen and Manuel Vega, "The Signal Processor System for the NASA Dual-Frequency Dual-Polarized Doppler Radar", IGARSS 2012, Munich.
• Kumar Vijay Mishra, V. Chandrasekar, Cuong Nguyen and Manuel Vega, "Waveform Design and Implementation for the Solid-State NASA Dual-Frequency Dual-Polarized Doppler Radar", IGARSS 2011, Vancouver.
• Jim George, Kumar Vijay Mishra, Cuong Nguyen and V. Chandrasekar, "Implementation of Blind Zone and Range-Velocity Ambiguity Mitigation for Solid-State Weather Radar", IEEE International Radar Conference, 2010, Washington DC.
• Nitin Bharadwaj, Kumar Vijay Mishra and V. Chandrasekar, "Waveform Considerations for Dual-Polarization Doppler Weather Radar with Solid-State Transmitters", IGARSS 2009, Cape Town
• Cuong M. Nguyen, V. Chandrasekar, Kumar Vijay Mishra, and J. George, "Sensitivity enhancement system for pulse compression weather radar", 35th AMS Conference on Radar Meteorology, 2011, Pittsburgh.
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Thank you
“See how that one little cloud floats like a pink feather from some gigantic flamingo. Now the red rim of the sun pushes itself over the London cloudbank.”
Sherlock Holmes’ observations on clouds The Sign of Four by Sir Arthur Conan Doyle, 1890
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