The LSM simulates the performance of coherent  Doppler wind lidars as space-based  remote sensors of winds  with an emphasis upon realistic representations of the atmosphere along individual line of sights. The MLSM version 1.0 optical property data bases supports a 2.053472 mm coherent Doppler wind lidar. 

Coherent DWL Signal Processing Model: Phi-Capon Method 

A simplified version of the Effective Gaussian Signal Spectrum Model (Frehilch and Sharman, 2003; Frehilch, 1997; Frehilch, 1996) is used to estimate the performance of a coherent DWL for general conditions in the threshold regime of weak signals.

The wide band SNR equation used in the LSM is defined as 

SNRW = (p×h₁×h₂×h₃×h₄×h₅×J×D²×l²  ß×e^-2óa(r)dr)/(8×hn×2×V_max×R²)

where

      h₁ - heterodyne quantum efficiency

      h₂ - transmit optical efficiency

      h₃ - receive optical efficiency

      h₄ - mixing efficiency

      h₅ - coherent system margin

        J - fundamental laser energy per pulse (Joules)

        D - mirror diameter (m)

        ß - backscatter (m^-1 sr^-1)

        e^-2óa(r)dr - 2 way attenuation

        hn - photon energy (J)

        R - slant range (m)

      l - laser wavelength (m)

        V_max - signal velocity bandwidth.

An effective wideband SNR (db) is computed by accumulating all the samples in an user's defined grid volume.

SNRW_eff =  10×log10( (S(SNRW_i)²)^0.5)

The number of data samples per LOS range gate is given as

m = (2.0 * d * 2.0 * V_max) / (c  * l * 1E-6)

where

       l - wavelength (m)

        V_max - maximum velocity measured

        c - speed of light (m/s)

        d - range gate (m).

Thus the effective photons per LOS range gate is 

f = m * SNRW_eff.

The percentage of bad estimates described by the following fraction of random outliers is

B = exp(-(0.1*f/B₀)^a)

where

        B₀ - constant

      a - constant

The percentage of bad estimates is used to decided whether the DWL performance produces a failed attempt, false alarm or a good wind measurement. If B is greater than the user's entry of the gross error probability threshold, then it is considered a failed attempt. If the performance is considered to be a "good" performance, then the estimates have a random chance of producing a false alarm in which f is set to 0.1. The line of sight uncertainty spread for the "good" estimates  is defined as

s_los = C * (1.0 + (f*0.1/G₀)**e)**(-d) + m 

where

        s_los - the line-of-sight uncertainty (m/s).

        X - constant

        G₀ - constant

      e - constant

      d - constant

       m - constant

Questions on the DWL Signal Processing Models mailto: Dave Emmitt 

Last Updated: 02/07/2007