Retrieving Cloud Optical Depth from Zenith Radiance Observations Examples from Pt' Reyes ARM Mobile

1
Retrieving Cloud Optical Depth from Zenith
Radiance Observations Examples from Pt. Reyes
ARM Mobile Facility

• Christine Chiu, UMBC/JCET
• Alexander Marshak, GSFC
• Yuri Knyazikhin, Boston University
• Warren Wiscombe, GSFC
• James Barnard, PNNL
• John Schmelzer, PNNL

2
(No Transcript)
3
Calibrate the 2NFOV using Goddard facility
sphere

• For the clean lens, difference of radiance
  between pre- and post-calibrations
• -- 2 for both RED NIR channels

4
For the dirty lens

• Compared to radiances from the clean lens, values
  for the dirty lens are
• RED -- 18 lower
• NIR -- 9 lower

5
Comparisons between 2NFOV MFRSR (overcast cases
using old calibration coeff.)
Retrievals from 2NFOV
Retrieved cloud optical depth from MFRSR
6
Comparisons between 2NFOV MFRSR (overcast cases
using new calibration coeff.)
Retrievals from 2NFOV
Retrieved cloud optical depth from MFRSR
7
Problem when the FOV is not entirely filled with
clouds
8
Comparison between 2NFOV and MWR retrievals for
cumulus clouds
9
Using the same idea, we can retrieve cloud
optical depth from Micro-Pulse Lidar

• Need a calibration factor

10
Cloud optical depth
Time (UTC)
11
Summary

• The REDvsNIR method retrieves cloud optical depth
  using zenith radiance
• Works in a fully 3D cloud situation
• Except 1) when the FOV is not entirely filled
  with clouds, and 2) cloud edge is illuminated by
  the sun.
• Micro-Pulse Lidar can be used as a NFOV
  radiometer if we can calibrate solar background
  signal.

12
Uncertainty analysis for REDvsNIR retrievals -
using 7 radiance uncertainty in RED and 3 in
NIR
standard deviation ? 5
13
(No Transcript)
14
Retrieval method - REDvsNIR
15
Retrieval method - REDvsNIR
Radiance
Cloud optical depth
16
(No Transcript)