Kippzonen Brewer MkIII Manual de usuario descargar pdf (Pagina 113)

MKIII OPERATOR'S MANUAL

110

COMPENSATING FOR DEADTIME

Poisson statistics are assumed so that for any observation at a true count rate F0 (counts/second)

the observed rate F will be

⋅−

⋅←

where T1 is the deadtime of the photon-counting system (as determined by the deadtime test, DT,

run as part of the Brewer setup procedures).

This equation is solved for F0 by iterating 9 times on the (rearranged) expression:

⋅

⋅←

This compensation is performed for each of the five operational wavelengths.

The deadtime-compensated count rates are normalized by computing the base-ten logarithm, then

scaled by 104, thus allowing integer arithmetic.

COMPENSATING FOR TEMPERATURE

The count rates are corrected for the temperature-dependent bandpass characteristics of

various filters inside the spectrometer assembly:

( )

6..2, =+⋅++← iAFTETCPCFF

piii

where

PC is the constant part of the temperature coefficient

TCi are the wavelength-dependent temperature coefficients read from the

spectrophotometer's Constants File (stored on disk)

TE is the instrument temperature in degrees Celsius

AFp is the attenuation value of the neutral-density filters at position p (the array AF

of attenuation values is also read from the instrument Constants File).

COMPENSATING FOR RAYLEIGH SCATTERING (DS ONLY)

If the reading is of the direct sun, the count rates are adjusted by compensating the effect of

Rayleigh-scattering attenuation for the airmass calculated for the time of the observation:

6..2,

1013

××

+← i

PZMBE

where

BEI are the Rayleigh coefficients.

PZ is the atmospheric pressure at the site of the instrument (in millibars)

1013 is standard atmospheric pressure (millibars)

M3 is the airmass (also referred to as the path-lengthening factor) for a layer of

height 5 km above the earth.

M3 is recalculated prior to each solar observation:

)])sin([sec(arcsin3 AkM ⋅←

where

A is solar zenith angle

k = R / (R + Z)

R is radius of earth (6370 km)

Z is layer height (5 km)

1 2 ... 108 109 110 111 112 113 114 115 116 117 118 ... 135 136

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