Atmospheric CO2 – Plots

All plots use parameters as listed unless noted [1]:

_CO2  =  380                _CO2  =  1.4e-23               H_CO2  =  5552
T_o  = 288.15         T[z]  =  T_o  –  650e-6 z

                 H is altitude (10 km) ;  z is length of total path: z = 2 h

  1) Optical path volume dependency: beam divergence ; lens radius r2 for fixed H = 10 km
      TX volume is PUR ;  RX volume in ORG.
Experimental value is = 0.17 mrad; r2 = 0.1 m

2) Optical depth over h (altitude) and nominal surface temperature.
     Transmitter path is BLU;
     RED is optical depth for TX at reflecting surface;
    GRN is along RX path

3) The instrument only “sees” the signal at the end of the RX travel path
    The optical depth vs surface temperature: BLU at reflecting surface; GRN at receiver (measured)

The GRN line represents a measurement at nominal CO₂ concentration (380 ppmv); the RED line represents an increase in CO₂ concentration of 1 ppmv (the desired measurement resolution)

Note that this is based on a temperature profile based on variation in surface temperature with no change in slope dependency in z

4) From:    =  _o exp [-]  where _o  =  1

In this ideal case – and if temperature were constant – this difference could be detected.

5) Detail of Figure 4

A variation of ±½K (~ 1°F) causes variation in received signal strength highlighted by colored polygons.

6) Normalized receive signal  from    =  exp [-] for variation

These plots represent the differential ratio; not absolute common-mode signal strength.

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[1] Physical constants obtained from NIST ;  spectral parameters derived from HITRAN2004/2008

That’s all for now.

Next 8: Basic Reflectivity & Range