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Comparison of two ALS-450 Algorithms

Comparison of two ALS-450 Algorithms. Ray Hoff, Kevin McCann, Ruben Delgado, Simone Lolli, Laurent Sauvage. Put name here. Leosphere ALS-450 Algorithm. Matches near 6 kilometers a section of profile which appears “Rayleigh-like” Uses a Klett backward retrieval to derive extinction

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Comparison of two ALS-450 Algorithms

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  1. Comparison of two ALS-450Algorithms Ray Hoff, Kevin McCann, Ruben Delgado, Simone Lolli, Laurent Sauvage Put name here

  2. Leosphere ALS-450 Algorithm • Matches near 6 kilometers a section of profile which appears “Rayleigh-like” • Uses a Klett backward retrieval to derive extinction • While the software allows choosing an aerosol type, we have not seen that the Sa changes in the extinction retrieval. Setting Sa in the Leosphere panels is not reflected in the retrieval files.

  3. UMBC’s modified retrieval • We use the Leosphere count profile, background corrected by their software • We search for a segment of clear air “Rayleigh-like” at 6-10 km for at least 1km segment. If the shape follows Rayleigh, we extend a Rayleigh profile based on USSA to the surface. • We use the exp (-2τ) from interpolation of 340 – 380 nm Cimel measurement at UMBC to estimate what the near surface return would be and this gives a system constant for the SA. K is monitored and if it doesn’t change from prior day by more than 5%, a retrieval is attempted. • Sa is iterated by scaling the profile to match the AOD. • Once Sa is fixed at the time of the calibration time, K and Sa do not change through the day.

  4. Explicitly

  5. K is supposed to be a constant

  6. Sanity checks • K for our system decreased from 0.17 when new (Aug 2009) to 0.11 in Aug 2010 when the laser quit. It is in for repair at this point. So we view K as a measure of system health. No power monitoring is available on ALS-450 • If lidar AOD is seen with clouds, we subtract the aerosol on both sides and estimate cloud AOD. We will compare this to the CIMEL cloud mode over the next year. • Ultimately, we need to compare ALEX Raman and Leosphere at 355, but my student is not progressing on this as fast as I had hoped.

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