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S-Polka. Remote Sensing Instruments. HIAPER Cloud radar. CSU-CHILL. NRL P-3 ELDORA. Microwave Temperature Profiler. HSRL on GV. Cloud Radar and Lidar Instruments for Sensing Aerosol and Clouds Vivek Earth Observing Laboratory NCAR, Boulder, Colorado.

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remote sensing instruments

S-Polka

Remote Sensing Instruments

HIAPER Cloud radar

CSU-CHILL

NRL P-3 ELDORA

Microwave Temperature Profiler

HSRL on GV

slide2

Cloud Radar and Lidar Instruments for Sensing Aerosol and Clouds

Vivek

Earth Observing Laboratory

NCAR, Boulder, Colorado

NCAR maintains and deploys a suite of world-class remote sensing instruments (radars and lidars) in support of the atmospheric science community

Develops innovative and state of the art “next-generation” remote sensors

motivation for observational instruments
Cloud:

Differences in cloud parametrizations lead to variations in climate model predictions

- cloud detection -optically thin clouds (-50 to -20 dBZ)

- cloud fraction without reference to optical depth

Cloud microphysics

- Phase

- size

Aerosol:

Aerosol type, concentration, size and shape

Motivation for Observational Instruments
background
Liquid droplets are classified into three categories based on size

Cloud droplet size < 50 mm

Drizzle droplet size is between 50 and 500 mm

Raindrop size > 500 mm

Scientific applications

Cloud radiation studies

Numerical weather prediction

In-flight aircraft icing

Background
scientific motivation
Cloud radiation studies

Influence of cloud on earth’s radiation budget is significant

(Heymesfield, 1993, Stephens 1999)

Radiation impact is quantified by droplet size, liquid water content, and cloud thickness (Stephens et al, 1998)

LWP= 2/3 * optical depth * effective radius

e.g. For a Cloud with an optical depth of 30 and

effective radius 10 mm, LWP = 200 g m-2

Even a small change in droplet size may cause large change in

Cloud albedo (Slingo, 1990)

Scientific Motivation
scientific motivation cont
Initiation of warm rain

Precipitation growth in a cumulus cloud is not well understood

There is a major difference in time scales of formation of

large drops between model and observation

( Knight et al., 2002)

e.g. Large drops appear in cloud base well before main burst of precipitation

Both observations and modeling of cloud droplet formation

need to be improved

Scientific Motivation (cont.)
limitation of radar reflectivity
Limitation of radar reflectivity
  • Problem of using radar to infer liquid water content:
    • Very different moments of a drop size distribution:
      • Reflectivity often dominated by drizzle drops ~100 mm
      • LWC dominated by ~10 m cloud droplets
  • An alternative is to use dual-wavelength radar
    • Radar attenuation proportional to LWC, increases with frequency
    • Radar reflectivity difference between two frequencies ( e.g. 3 and 35 GHz) is proportional to LWC with no size assumptions necessary
  • Dual-wavelength radar method can be difficult to implement in practice
    • Need very precise radar measurements
slide8

drizzle

“transition” drizzle

A million droplets of 10 mm

give the same radar reflectivity as

one droplet of 100 mm!

A million droplets of 10 mm contain

a thousand times as much water

as one one droplet of 100 mm.

And so: one drizzle droplet changes the

reflectivity significantly without changing

the liquid water content

cloud droplets

Ref: Herman Russchenberg, and Oleg Krasnov, 2004

hcr characteristics
Scanning, airborne, W-band Doppler radar for Gulfstream V (GV) mid-altitude jet (51kft ceiling)

Phase A: system to be ready for test flights in Summer 2011

Phase B: Adds Polarimetry (H-V), pulse compression – unfunded

Phase C: Adds Second wavelength (Ka-band) – unfunded

Initial system design incorporates electro-mechanical infrastructure of phases B and C

Radar electronics housed in un-pressurized wing-mounted pod, with data archiving and real-time display inside aircraft

HCR Characteristics
ground based configuration
Ground-based Configuration

LWC ~ 0.05 – 0.1 g m-3

C-130

rain rate estimation
Rain rate estimation

Matrosov, 2007, GRL

slide15

HSRL on the NCAR Gulf Stream-V Research Aircraft

Technical Specifications:

Wavelength: 532 nm

Pulse repetition rate: 6 KHz

Average power: up to 400 mW

Range resolution: 7.5 m

Telescope diameter: 40 cm

Angular field of view 0.025 deg

Filter bandwidth: 1.8 GHz

gv hsrl measurements of aerosol and smoke at ncar s foothills campus on september 6 2010
GV HSRL measurements of aerosol and smoke at NCAR’s Foothills campus on September 6, 2010
high spectral resolution lidar and mm wave radar
High Spectral Resolution Lidar and mm-wave radar
  • GV HSRL Designed and built by University of Wisconsin – Madison
  • Provides accurate measurement of optical depth, extinction and backscatter cross sections of aerosols and thin clouds
  • Eye-safe at the exit port (532-nm wavelength operation)
  • GV HSRL is already operational operation as ground based instrument
  • To be used to in combination with HCR to measure:
    • cloud fraction, precipitation rate, scattering cross sections, particle shape

measurements on 1-Oct of 2008 by the arctic HSRL and MMCR

Courtesy of University of Wisconsin

summary
Lidar operates in 24/7 mode

W-band radar development will be completed in

12 months

Data quality - Calibration

Retrieval of microphysical products from radar measurements

Retrieval of aerosol and cloud products from lidar measurements

Retrieval of aerosol and cloud microphysical products using both radar and lidar measurements

Summary
scientific motivation cont1
Aircraft icing

Inflight icing is caused by impingement of supercooled droplets onto an aircraft

Median volume diameter > 30 mm and LWC > 0.2 gm-3

cause hazardous icing condition (Politovich, 1989)

Percentage of ice accretion ( or catch ratio) onto an airplane depend on liquid particle size

Detection of droplets in a mixed phase cloud is much more challenging

Scientific Motivation (cont.)
slide32

Retrieval of particle size (RES), LWC from Ka-band reflectivity and microwave Radiometer observations.

slide33

+ In-situ

Radar

Altitude, m

Liquid water content, g m-3

Comparison of liquid water content between radar/radiometer retrievals and in-situ measurements during WISP04. In-situ measurements are from a liquid water probe on board the UND Citation research aircraft.

slide34

Liquid water content, g m-3

Size, mm

Field Experiments

Field Experiments

Distributions of a) LWC and b) RES and MVD that were computed from in situ research aircraft measurements at various field programs. The top and bottom of each box is the 10th and 90th percentiles of the measurement set; the middle solid line is the median (50th percentile); dashed internal lines are the 25th and 75th percentiles. The numbers of samples are listed at the tops of the boxes.

system calibration
Absolute Calibration

Corner reflector

Sea surface

Noise/signal sources used to measure gain and dynamic range of the receiver

Dynamic Calibration

Transmitted signal continuously switched into the receiver during operation while the radar is “blind”

Noise floor measurement possible periodically during aircraft turns, etc.

System Calibration
pod based radar system layout1
Pod Based Radar System Layout

Pod:

Length = 158.5”

Diameter = 20”

Payload = 800 lbs

  • Extended Interaction Klystron Amplifier (EIKA)
  • Based on the rugged, reliable Klystron
  • Conduction cooled, similar to version produced for CloudSat
liquid water content verses reflectivity
Liquid water content verses reflectivity

K

B

A

Compilation of various aircraft observations from Khain et al. (2008, JAMC)

LWC computed from dual-wavelength (S- and Ka-band) radar

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