ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-6699-2010 Tomographic retrieval of cloud liquid water fields from a single scanning microwave radiometer aboard a moving platform – Part 2: Observation system simulation experiments Huang D. 1 Gasiewski A. 2 Wiscombe W. 1 3 Brookhaven National Laboratory, Upton, NY 11973, USA University of Colorado, Boulder, CO 80309, USA NASA Goddard Space Flight Center (Code 913), Greenbelt, MD 20771, USA 22 07 2010 10 14 6699 6709 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/6699/2010/acp-10-6699-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/6699/2010/acp-10-6699-2010.pdf

Part 1 of this research concluded that many conditions of the 2003 Wakasa Bay experiment were not optimal for the purpose of tomographic retrieval. Part 2 (this paper) then aims to find possible improvements to the mobile cloud tomography method using observation system simulation experiments. We demonstrate that the incorporation of the <i>L</i><sub>1</sub> norm total variation regularization in the tomographic retrieval algorithm better reproduces discontinuous structures than the widely used <i>L</i><sub>2</sub> norm Tikhonov regularization. The simulation experiments reveal that a typical ground-based mobile setup substantially outperforms an airborne one because the ground-based setup usually moves slower and has greater contrast in microwave brightness between clouds and the background. It is shown that, as expected, the error in the cloud tomography retrievals increases monotonically with both the radiometer noise level and the uncertainty in the estimate of background brightness temperature. It is also revealed that a lower speed of platform motion or a faster scanning radiometer results in more scan cycles and more overlap between the swaths of successive scan cycles, both of which help to improve the retrieval accuracy. The last factor examined is aircraft height. It is found that the optimal aircraft height is 0.5 to 1.0 km above the cloud top. To summarize, this research demonstrates the feasibility of tomographically retrieving the spatial structure of cloud liquid water using current microwave radiometric technology and provides several general guidelines to improve future field-based studies of cloud tomography.

 References % vor jede Referenz Acar, R. and Vogel, C. R.: Analysis of total variation penalty methods, Inv. Prob., 10, 1217–1229, 1994. Ackerman, S. A., Toon, O. B., and Hobbs, P. V.: A model for particle microphysics, turbulent mixing, and radiative transfer in the stratocumulus topped marine boundary layer and comparisons with measurements, J. Atmos. Sci., 52, 1204–1236, 1995. Chambolle, A. and Lions, P. L.: Image recovery via total variation minimization and related problems, Numer. Math., 72, 167–188, 1997. Drake, J. F. and Warner, J.: A theoretical study of the accuracy of tomographic retrieval of cloud liquid with an airborne radiometer, J. Atmos. Sci. Ocean. Tech., 5, 844–857, 1988. Falcone, V.: Calculation of apparent sky temperature at millimeter wavelengths, Radio Sci., 1 (new series), 1205–1209, 1966. Frisch, A. S., Fairall, C. W., and Snyder, J. B.: Measurement of stratus cloud and drizzle parameters in ASTEX with a Ka-band Doppler radar and a microwave radiometer, J. Atmos. Sci., 52, 2788–2799, 1995. Gordon, R., Bender, R., and Herman, G. T.: Algebraic Reconstruction Techniques (ART) for Three-dimensional Electron Microscopy and X-ray Photography, J. Theor. Biol., 29, 471–481, 1970. Hansen, P. C.: Rank deficient and ill-posed problems: Numerical aspects of linear inversion, SIAM, Philadelphia, 247~pp., 1998. Hogan, R. J., Gaussiat, N., and Illingworth, A. J.: Stratocumulus liquid water content from dual-wavelength radar, J. Atmos. Ocean. Tech., 22, 1207–1218, 2005. Huang, D., Liu, Y., and Wiscombe, W.: Determination of cloud liquid water distribution using 3D cloud tomography, J. Geophys. Res., 113, D13201, doi:10.1029/2007JD009133, 2008a. Huang, D., Liu, Y., and Wiscombe, W.: Cloud tomography: Role of constraints and a new algorithm, J. Geophys. Res., 113, D23203, doi:10.1029/2008JD009952, 2008b. Huang, D., Gasiewski, A. J., and Wiscombe, W.: Tomographic retrieval of cloud liquid water fields from a single scanning microwave radiometer aboard a moving platform – Part~1: Field trial results from the Wakasa Bay experiment, Atmos. Chem. Phys., 10, 6685–6697, doi:10.5194/acp-10-6685-2010, 2010. Johnson, J. T.: An efficient two-scale model for the computation of thermal emission and atmospheric reflection from the sea surface, IEEE T. Geosci. Remote., 44, 560–568, 2006. Liljegren, J., Clothiaux, E., Mace, G., Kato, S., and Dong, X.: A new retrieval for cloud liquid water path using a ground-based microwave radiometer and measurements of cloud temperature, J. Geophys. Res., 106(14), 485–500, 2001. Lobl, S. E., Aonashi, K., Griffith, B., Kummerow, C., Liu, G., Murakami, M., and Wilheit, T.: Wakasa Bay – An AMSR Precipitation Validation Campaign, Bu. Am. Meteorol. Soc., 88, 551–558, 2007. Pederson, J.: Modular Algorithms for Large–Scale Total Variation Image Deblurring. Technical University of Denmark, master thesis, 122~pp., 2005. Rosenkranz, P. W.: Water vapor microwave continuum absorption: A comparison of measurements and models, Radio Sci., 33(4), 919–928, doi:10.1029/98RS01182, 1998. Strong, D. and Chan, T. F.: Edge-preserving and scale-dependent properties of the total variation regularization, Inverse Problems, 19, 165–187, 2003. Stephens, G. L.: Cloud feedbacks in the climate system: a critical review, J. Climate, 18, 237–273, 2005. Twomey, S.: Introduction to the mathematics of inversion in remote sensing inversion and indirect measurements, Elsevier, Amsterdam, 243~pp., 1977. Twomey, S.: Iterative nonlinear inversion methods for tomographic problems, J. Atoms. Sci., 44, 3544–3551, 1987. Warner, J., Drake, J. F., and Krehbiel, P. R.: Determination of cloud liquid water distribution by inversion of radiometric data, J. Atmos. Ocean. Tech., 2, 293–303, 1985. Warner, J., Drake, J. F., and Snider, J. B.: Liquid water distribution obtained from coplanar scanning radiometers, J. Atmos. Ocean. Tech., 3, 542–546, 1986. Warner, J. and Drake, J. F.: Field tests of an airborne remote sensing technique for measuring the distribution of liquid water in convective cloud, J. Atmos. Ocean. Tech., 5, 833–843, 1988. Weare, B. C.: Evaluation of the vertical structure of zonally-averaged cloudiness and its variability in the Atmospheric Model Intercomparison Project, J. Climate, 9, 3419–3431, 1996. Westwater, E. R.: Microwave emission from clouds, NOAA Tech. Rep. ERL 219-WPL, 18, 43~pp., 1972. Westwater, E. R., Crewell, S., and Matzler, C.: A review of surface based microwave and millimeter wave radiometric remote sensing of the troposphere, Radio Sci. Bull., 3010, 59–80, 2004.