Solid-state weather radar pulse compression receiver and...

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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• 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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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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MS Final Exam

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




Weather Radars



• NASA D3R System


• 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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MS Final Exam

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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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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MS Final Exam

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




Weather Radars



• NASA D3R System


• 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




Weather Radars



• NASA D3R System


• Summary

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• 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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MS Final Exam

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

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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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MS Final Exam

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




Weather Radars



• NASA D3R System


• Summary

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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

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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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MS Final Exam

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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




Weather Radars



• NASA D3R System


• 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)

51/61 Comparison of D3R and WKR (Chandrasekar et. al., "Dual-Frequency Dual-Polarized Doppler Radar (D3R) System for GPM Ground Validation: Update and Recent Field

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




Weather Radars



• NASA D3R System


• 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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