Worldwide assessments of laser radar tactical scenario performance variability for diverse low altitude atmospheric conditions at 1.0642 μm and 1.557 μm

Abstract

Spatial, spectral and temporal variations in operating conditions are major contributors to the expected variability/uncertainty in system performance. The ratio of signal-to-noise ratio (SNR) based on climatological data to a standard atmosphere is the primary performance metric used, with results presented in the form of histograms and maps of worldwide LADAR performance variation. This metric is assessed at 2 wavelengths, 1.0642 µm and 1.557 µm, for a number of widely dispersed land and maritime locations worldwide over oblique and vertical air to surface paths in which anticipated clear air aerosols and location specific heavy rain and 150 m thick fog occur. Seasonal, boundary layer, and time of day variations for a range of relative humidity percentiles are also considered. In addition to realistic vertical profiles of molecular and aerosol extinction, air-to-ground cloud free line of sight (CFLOS) probabilities as a function of location for this geometry are computed. Observations from the current study strongly indicate that use of the standard atmosphere to predict performance will produce overly optimistic, in many cases extremely so, estimates of expected performance. Locally heavy rain, when present, severely limits LADAR system performance at these wavelengths. Some operational capability exists for vertical looks through fog.

Worldwide uncertainty assessments of ladar and radar signal-to-noise ratio performance for diverse low altitude atmospheric environments

“…Higher wind speeds over ocean areas generate more sea salt aerosols; these aerosols are hygroscopic and tend to become larger as RH approaches 100%. High wind speeds and high RHs combine to create higher aerosol concentrations and larger size distributions over the high ocean latitudes [2]. The land/ocean composite comparisons seen in Fig.…”

“…This difference in boundary layer height means that over the oceans a significant portion of the oblique path is located in the free atmosphere above the boundary layer, while over the land the path is entirely within the boundary layer. The free atmosphere is defined in HELEEOS by six different generally latitude-dependent standard atmospheres [2,7]. Each standard or reference atmosphere has a summer and winter variant.…”

“…Its basic features have been previously described [1]. A key component of HELEEOS is a worldwide probabilistic model of spatial and temporal variations in atmospheric characteristics which has been described in detail [2,3,4]. This atmospheric model spans wavelengths from the visible to radio frequencies.…”

“…The 0.02 percent threshold was chosen because it is in the middle of the range of "percent of year" values computed for the original Crane and Blood study. The minimum heavy rain rate at the 99.98th percentile level is 12 mm h -1 and the maximum is 115 mm h -1 [2]. percentile relative humidity conditions, for January, for 3000 meter slant range oblique case in the presence of locally extremely heavy rate, with the location-specific rate set as indicated in Fig.…”

Modeling bistatic spectral measurements of temporally evolving reflected and emitted energy from a distant and receding target

“…The atmospheric parameters investigated, such as temperature, pressure, water vapor content, optical turbulence, and atmospheric particulates, are put into vertical profiles of data for highly specific modeling scenarios. The worldwide seasonal, diurnal, and geographically varying databases, covering all land and ocean regions underlying the HELEEOS atmospheric model, have been described in earlier publications, 1,6,7 and are available in a stand-alone atmospheric characterization software code called the Laser Environmental Effects Definition and Reference (LEEDR). 8 For the Remote Observer Scenario Toolkit, AFIT/CDE incorporates a single scattering path radiance calculation capability into the HELEEOS atmospheric computational engine.…”