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New sensors and models for complex environmental conditions. John N. Porter University of Hawaii. If one cannot accurately measure the in situ optical properties of the environment, then developing a satellite remote sensing algorithm is like trying to hit a target with poor vision

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Presentation Transcript
slide2
If one cannot accurately measure the in situ optical properties
  • of the environment, then developing a satellite remote sensing
  • algorithm is like trying to hit a target with poor vision
    • Hard to see the target
    • (you will use inadequate/incorrect algorithms),
    • 2) Hard to see if you hit the target
    • (difficult to determine if your results are correct)

While new satellite algorithms are moving forward,

more effort is needed for environmental optical characterization.

what is still missing in our environmental optical toolbox
What is still missing in our environmental optical toolbox ?
  • 1) Aerosol Polar Nephelometer
  • 2) Automatic Sun-Sky Photometer for use on ships and aircraft
  • 3) Monte Carlo radiative transfer programs which can deal with land,
  • ocean and atmosphere inhomogeneity
  • 4) All-sky camera network to map out spatial distribution of clouds
  • We are now working on these problems.
slide4
Ground-based aerosol polar nephelometer

Modified to make polarization measurements

Field measurements planned for summer.

Sea salt phase function

(unpolarized light)

UAE dust/pollution phase function

(vertical and depolarization)

slide5
Mini custom polar nephelometer

- Tried various approaches with low cost components

- System still under testing with more expensive components

slide6
Aircraft handheld sun photometer measurements

Many bad values must be removed!

Aircraft

Height

Agreement with ground Cimel

Porter, J.N. A. Clarke, J. Reid, G. Shaw, H. Maring, E. Reid, D. Kress, Handheld Sun Photometer Measurements From Light Aircraft, J. Atmos. Ocean. Tech., 24, 1588-1597, 2007.

slide7
WebCam Sun-Sky Photometer (WCSSP) (for ships and aircraft)Basic design already tested, now incorporating faster components
calibration of new automatic sun sky photometer at mlo hawaii
Calibration of new automatic sun-sky photometer (at MLO, Hawaii)

Beers Law

I = Io exp(- τ /cos(θ)

(define AirMass = 1/cos(θ) )

V = Vo exp(-τ AirMass)

ln(V) = - τ AirMass + ln(Vo)

determine Vo by extrapolating to zero air mass

New sun-sky photometer system tracked sun automatically on several days with

excellent results. The concept of using webcams for sun alignment works well. The

System upgrades for faster performance are near completion.

slide9
A new Monte Carlo radiative transfer model (AO3D). To study light fields in complex cases with inhomogeneous conditions

Example of complex coastal site (UAE 2, MAARCO site)

slide10
AO3D tracks photons through the atmosphere-ocean

and uses Monte Carlo techniques to solve radiation

problems.

AO3D accounts for:

ocean surface roughness and whitecaps

multiple aerosol layers

refraction (index of refraction layer changes)

earth curvature

user specified optical properties

AO3D compares well with

Modtran4

COART

Kattawar and Adams

Bates, D. and J. Porter, AO3D: A Monte Carlo Code for Modeling of Environmental Light Propagation, accepted in Journal of Quantitative Spectroscopy and Radiative Transfer, January 2008.

slide12
AO3D model of laser beam entering ocean.

Points show where photon was absorbed

slide13
Monte Carlo time-resolved calculations.

AO3D compared with lidar equation.

Standard Lidar Eq. (green)

Monte Carlo simulation (blue)

slide14
AO3D top of the atmosphere radiance compared with Kattawar and Adams (1978)

Kattawar and Adams (circles)

AO3D (triangles)

Calculations of total-scatter TOA radiance for spherical-shell molecular atmosphere with no surface reflection.

calculation of height of aerosol layer over mauna loa observatory
Calculation of height of aerosol layer over Mauna Loa Observatory

Sun photometer measurements

made at Mauna Loa

Observatory using new

automated sun tracking sun

photometer out to air mass

20 (small dots). Larger dots

show expected values

calculated with AO3D Monte

Carlo radiation model for

aerosol layer placed at different

heights.

Best agreement is

found when aerosol layer is

placed slightly above the

observatory. Only coarse aerosol

positioning was attempted. Further

studies could provide a better fit.

Bates and Porter, 2007

slide16
AO3D Monte Carlo code showing that an inhomogeneous surface has a significant impact on sky radiance.

Land | Ocean

Tropical Atmosphere

Sulfate Aerosols

SZA = 60deg

Figure above shows sky radiance for a coastal site

with part of the sky over land and the other over

ocean. Three different aerosol optical depths are

shown. Surface inhomogeneity turns out to

significantly affect the sky radiance for all aerosol

loadings ! (unpublished results)

Example of Azimuth Angle Scan

cloud mapping stereo camera system
Cloud Mapping Stereo Camera System

Cloud cover, cloud shape, cloud microphysical properties, and location all affect surface and satellite radiation measurements. In order to model these light fields it is therefore important to quantify cloud properties as much as possible.

In addition to radiation problems, there is also a need for new wind measurements aloft where little data exists. Cloud tracking can be used to derive winds aloft.

For these reasons we have begun testing a new approach to map out cloud fields and to derive wind fields at different heights using ground based stereo cameras.

slide19
Calculation of

relative wind

speed based on

feature tracking

with spatial

correlation.

Wind vectors

calculated from

two images

and overlain

on one of the

images.

slide20
Cloud simulation model to test how far apart the stereo cameras need to

be and what the accuracy is needed for camera azimuth and zenith angles.

(work in progress)

slide21
In order to derive cloud position accurately from stereo cameras, we need to know the camera internal and external calibrations (azimuth and zenith angles for each pixel). Internal calibration was carried out with a reference pattern and an example is shown on the right.

External calibration is achieved by external reference points. To be discussed in detail in the

future publication.

slide22
In order to test the camera internal calibration we carried out a set of independent measurements using a pan-tilt system. A single bright light source was placed ~80 m away and the camera was panned and tilted under computer control. Preliminary results are shown below. The error seen in the azimuth angle figure is likely due to cases with near zero zenith angle (azimuth angle poorly defined). (work in progress)

Camera on pan-tilt

System.

Two different camera angular calibration

approaches plotted versus each other.

conclusion
Conclusion
  • Good progress is occurring in each of these 4 areas and new papers will
  • be appearing soon.
  • Aerosol Polar Nephelometer
  • 2) Automatic Sun-Sky Photometer for use on ships and aircraft
  • 3) Monte Carlo radiative transfer programs which can deal with land,
  • ocean and atmosphere inhomogeneity
  • All-sky camera network to map out spatial distribution of clouds
  • and wind speeds.
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