Air mass parameterization and coastal aerosol modeling

1997 
Abstract The United States Navy is increasingly concerned with operations in coastal environments. One key threat to ships is the easily launched high precision anti-ship weaponry readily available in the world-arms market. Fleet units operating in either the open ocean or in coastal regions must be able to determine the standoff ranges at which they can detect and/or track such sophisticated weaponry. The Navy is presently developing and utilizing infrared (IR) technology for the detection and identification of such threats. Atmospheric aerosol extinction, refraction, turbulence and infrared sea and terrain background models in LOWTRAN and MODTRAN are presently inadequate for representing IR propagation close to the ocean surface and in coastal environments. This requires accurate models to describe the effects of low level ocean and coastal aerosols to be incorporated into LOWTRAN and MODTRAN for determining the performance of EO systems used for detecting these low-altitude targets. Not much is known concerning the coastal air mass characteristics required for advanced aerosol modeling. Since the diverse air mass transitions that frequent coastal environments may have profound effects upon aerosol properties and EO propagation, a good assessment of the NAM/NOVAM air mass parameter for coastal applications is essential. The NAM/NOVAM dN/dr aerosol size distribution model consists of three log normal distributions, the first component being scaled proportionate to the square of the air mass parameter (AMP). Therefore, when using NAM/NOVAM for calculating extinction coefficients and optical depths in the MBL, the AMP is the most critical input parameter and is, of course, the most difficult to obtain. Several techniques are being evaluated or utilized to obtain this parameter including air mass trajectory analysis, radon, condensation nuclei, and multiple wavelength nephelometer measurements. All of these techniques are in-situ measurements for a given geographic location. When considering the complexity and variability of the air mass characteristics within a coastal environment, an alternate remote sensing technique for determining the AMP must be determined for NAM/NOVAM to be applicable for coastal application. The purpose of this paper is to present an alternative approach for determining the surface AMP from satellite upwelling radiance measurements, LOWTRAN, and the NOVAM aerosol model. Using satellite detected upwelling radiance measurements, multiple wavelength satellites, such as the NOAA -14 AVHRR, can be used to determine the total atmospheric aerosol optical depth (OD Sat ) and its geographical variability. Utilizing this satellite OD data base and the LOWTRAN calculated OD (OD LOWTRAN ) for tropospheric aerosol scatter above the marine boundary layer (MBL), the contribution to the total aerosol OD Sat by the boundary layer (OD MBL ) for a geographic location can be determined by subtracting these two values, e.g., OD MBL = OD Sat - OD LOWTRAN . The AMP associated with this OD (OD MBL ) can then be related to the NAM/NOVAM aerosol model by exercising NAM/NOVAM as a function of AMP until the NAM/NOVAM calculated OD (OD NOVAM ) agrees with that required from the satellite observation for the MBL. The resulting AMP represents that required as an input to NAM/NOVAM for predicting the IR propagation characteristics within the MBL as a function of wavelength for a specific geographic location and time.
    • Correction
    • Source
    • Cite
    • Save
    • Machine Reading By IdeaReader
    0
    References
    1
    Citations
    NaN
    KQI
    []