Remote sensing instruments
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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

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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


Remote sensing instruments

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


Remote sensing instruments

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


Pod based radar system layout

Pod Based Radar System Layout


Ground based configuration

Ground-based Configuration

LWC ~ 0.05 – 0.1 g m-3

C-130


Measurement of vertical air velocity

Measurement of vertical air velocity


Remote sensing instruments

Kollias et al., 2002, BAMS.


Rain rate estimation

Rain rate estimation

Matrosov, 2007, GRL


Remote sensing instruments

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


Remote sensing instruments

Backscatter cross section as a function of time and altitude.


Remote sensing instruments

Depolarization ratio as a function of time and altitude


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


Gv hsrl measurements of aerosols and clouds

GV HSRL measurements of aerosols and clouds


Model calculations of scattering

Model calculations of scattering.


Model calculation lidar backscatter cross section verses liquid water content

Model calculation: Lidar backscatter cross section verses liquid water content


Model calculation median volume diameter verses lidar ratio

Model calculation: Median volume diameter verses Lidar Ratio


Estimation of liquid water content

Estimation of Liquid water content


Cloud particle size estimation using radar and lidar measurements

Cloud particle size estimation using radar and lidar measurements


Estimation of liquid water content using radar and lidar measurements

Estimation of liquid water content using radar and lidar measurements


Hcr with high spectral resolution lidar hsrl

HCR with High Spectral Resolution Lidar (HSRL)


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


Model calculation lidar backscatter cross section verses liquid water content1

Model calculation: Lidar backscatter cross section verses liquid water content


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.)


Marshall test site

Marshall Test Site


Remote sensing instruments

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


Remote sensing instruments

+ 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.


Remote sensing instruments

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.


Model calculation median volume diameter verses lidar ratio1

Model calculation: Median volume diameter verses Lidar Ratio


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


Conversion of radar crosssection to dbz

Conversion of radar crosssection to dBZ


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