Modelling radar and lidar Modelling radar and lidar multiple scattering multiple scattering Robin Hogan • The CloudSat radar and the Calipso lidar were launched on 28 th April 2006 as part of the A-train of satellites • They represent an opportunity to retrieve the vertical profile of cloud properties globally for the first time: important for climate • But multiple scattering presents a problem in interpreting both the radar and the lidar signals
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Modelling radar and lidar multiple scattering Modelling radar and lidar multiple scattering Robin Hogan The CloudSat radar and the Calipso lidar were launched.
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Modelling radar and lidar Modelling radar and lidar multiple scatteringmultiple scattering
Robin Hogan
• The CloudSat radar and the Calipso lidar were launched on 28th April 2006 as part of the A-train of satellites
• They represent an opportunity to retrieve the vertical profile of cloud properties globally for the first time: important for climate
• But multiple scattering presents a problem in interpreting both the radar and the lidar signals
Eastern RussiaJapanSea of JapanEast China Sea
• Calipso lidar (<r)
• CloudSat radar (>r)
Molecular scattering
Aerosol from China?
CirrusMixed-phase
altocumulus
Drizzling stratocumulus
Non-drizzling stratocumulus
Rain
7 June 2006
5500 km
1D variational method1D variational methodNew ray of dataFirst guess of x
Forward modelPredict measurements y and Jacobian H from state vector x using forward model H(x)
Compare measurements to forward modelHas the solution converged?2 convergence test Gauss-Newton iteration step
Predict new state vector: xi+1= xi+A-1{HTR-1[y-H(xi)]
+B-1(b-xi)}where the Hessian is
A=HTR-1H+B-1
Calculate error in retrievalThe solution error covariance matrix is S=A-1
No
Yes
Proceed to next ray
– In this problem, the observation vector y and state vector x are:
n
n
N
N
ln
ln
ln
ln
1
1
x
m
mZ
Z
ln
ln 1
1
y
Examples of multiple Examples of multiple scatteringscattering
• LITE lidar on the space shuttle in 1994– Large detector footprint (300 m) means that photons may be scattered many
times and still remain within the field-of-view– The long path-length means that those detected appear to have been scattered
back from below cloud base (or below the surface)
• Need a sophisticated lidar forward model to represent this