Active cavity radiometer type IV

Richard C. Willson

doi:10.1364/AO.18.000179

Applied Optics
Vol. 18,
Issue 2,
pp. 179-188
(1979)
•https://doi.org/10.1364/AO.18.000179

Active cavity radiometer type IV

Richard C. Willson

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Richard C. Willson, "Active cavity radiometer type IV," Appl. Opt. 18, 179-188 (1979)

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Abstract

A new cavity pyrheliometer, the active cavity radiometer type IV (ACR IV), has been developed for the measurement of total solar optical irradiance. Analysis predicts its ability to measure at the solar constant level with 0.1% uncertainty in SI units. In comparison tests ACR IVs have consistently demonstrated 0.3% higher results than the World Radiometric Reference scale. A prototype has been tested, and a flight instrument has been developed and flown in a sounding rocket experiment to determine the solar constant. ACR IV instrumentation is being developed for flight experiments on the Spacelab I and Solar Maximum missions to monitor the total solar output of optical radiation as part of a long-term program to detect variations of climatological significance.

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Instrument	Developer	Mean performance relative to WRR (%)
ACR 310	Willson (U.S.A.)	+0.04
PMO 2	Fröhlich (Switzerland)	+0.10
ACR 311	Willson (U.S.A.)	+0.11
PACRAD III	Kendall (U.S.A.)	−0.19
CROM	Crommelynk (Belgium)	−0.20

Symbol	Units	Value	Uncertainty(±)	Description of parameter
α_c	—	0.9995	0.0003	Cavity absorptance
R	KΩ	0.500	0.00005	Cavity heater resistance
A_c	cm²	0.500	0.00013	Area of primary aperture
ρ_c	—	0.0005	0.0003	Cavity reflectance
ρ	—	0.05	0.02	Reflectance of cavity’s FOV
V_o	V	3.736	0.0009	Cavity heater voltage (observation phase)
V_r	V	7.223	0.0009	Cavity heater voltage (reference phase)
K_ti	mW/K	100	0.4	Conductance of thermal impedance
K_c₁	mW/K	0.1	0.01	Conductance of cavity electrical leads
σ	mW-cm⁻² K⁻⁴	5.6697 × 10⁻⁹	0.0007 × 10⁻⁹	Stefan-Boltzmann constant
C	W-sec-K⁻¹	0.5	0.05	Cavity heat capacity
∊_c_1,_c_2,_c₃	—	0.98	0.02	Cavity emittance to FOVs 1,2,3
∊_c_4,_c₅	—	0.05	0.03	Cavity emittance to FOVs 4,5
A_c_1,_c₂	cm²	0.5	0.00013	Cavity area seen by FOVs 1,2
A_c₃	cm²	1.3	0.13	Cavity area seen by FOV 3
A_c_4,_c₅	cw²	5.0	0.5	Cavity area seen by FOVs 4,5
∊₁	—	0.05	0.03	Emittance of FOV 1 (Ref. 17)
∊_2,3	—	0.95	0.03	Emittance of FOVs 2,3
∊₄	—	0.2	0.1	Emittance of FOV 4
∊₅	—	0.3	0.1	Emittance of FOV 5
T_c	K	301	10.0	Temperature of cavity
T_1,2,3,5	K	300	10.0	Temperature of FOVs 1,2,3,5 (Ref. 17)
T₄	K	300.5	10.0	Temperature of FOV 4
δT_c	K	0.01	—	Temperature drift (per cycle) of cavity
δT₁	K	10.0	—	Temperature drift (per cycle) of FOV 1
δT_2,3,4,5	K	0.02	—	Temperature drift (per cycle) FOVs 2–5
K_a₁	W/K	1 × 10⁻⁶	1 × 10⁻⁶	Air conductance from cavity to FOV 1
K_a₂	W/K	1.5 × 10⁻⁵	1 × 10⁻⁵	Air conductance from cavity to FOV 2
K_a₃	W/K	10⁻³	10⁻³	Air conductance from cavity to FOV 3
K_a₄	W/K	5 × 10⁻³	2 × 10⁻³	Air conductance from cavity to FOV 4
K_a₅	W/K	10⁻⁵	0.5 × 10⁻⁵	Air conductance from cavity to FOV 5
F_c₁	—	8 × 10⁻²	5 × 10⁻⁴	View factor between cavity and FOV 1
F_c₂	—	0.923	6 × 10⁻⁵	View factor between cavity and FOV 2
F_c₃	—	0.704	5 × 10⁻²	View factor between cavity and FOV 3
F_c₄	—	0.8	0.08	View factor between cavity and FOV 4
F_c₅	—	0.2	0.02	View factor between cavity and FOV 5

Instrument	Developer	Mean performance relative to WRR (%)
ACR 310	Willson (U.S.A.)	+0.04
PMO 2	Fröhlich (Switzerland)	+0.10
ACR 311	Willson (U.S.A.)	+0.11
PACRAD III	Kendall (U.S.A.)	−0.19
CROM	Crommelynk (Belgium)	−0.20

Symbol	Units	Value	Uncertainty(±)	Description of parameter
α_c	—	0.9995	0.0003	Cavity absorptance
R	KΩ	0.500	0.00005	Cavity heater resistance
A_c	cm²	0.500	0.00013	Area of primary aperture
ρ_c	—	0.0005	0.0003	Cavity reflectance
ρ	—	0.05	0.02	Reflectance of cavity’s FOV
V_o	V	3.736	0.0009	Cavity heater voltage (observation phase)
V_r	V	7.223	0.0009	Cavity heater voltage (reference phase)
K_ti	mW/K	100	0.4	Conductance of thermal impedance
K_c₁	mW/K	0.1	0.01	Conductance of cavity electrical leads
σ	mW-cm⁻² K⁻⁴	5.6697 × 10⁻⁹	0.0007 × 10⁻⁹	Stefan-Boltzmann constant
C	W-sec-K⁻¹	0.5	0.05	Cavity heat capacity
∊_c_1,_c_2,_c₃	—	0.98	0.02	Cavity emittance to FOVs 1,2,3
∊_c_4,_c₅	—	0.05	0.03	Cavity emittance to FOVs 4,5
A_c_1,_c₂	cm²	0.5	0.00013	Cavity area seen by FOVs 1,2
A_c₃	cm²	1.3	0.13	Cavity area seen by FOV 3
A_c_4,_c₅	cw²	5.0	0.5	Cavity area seen by FOVs 4,5
∊₁	—	0.05	0.03	Emittance of FOV 1 (Ref. 17)
∊_2,3	—	0.95	0.03	Emittance of FOVs 2,3
∊₄	—	0.2	0.1	Emittance of FOV 4
∊₅	—	0.3	0.1	Emittance of FOV 5
T_c	K	301	10.0	Temperature of cavity
T_1,2,3,5	K	300	10.0	Temperature of FOVs 1,2,3,5 (Ref. 17)
T₄	K	300.5	10.0	Temperature of FOV 4
δT_c	K	0.01	—	Temperature drift (per cycle) of cavity
δT₁	K	10.0	—	Temperature drift (per cycle) of FOV 1
δT_2,3,4,5	K	0.02	—	Temperature drift (per cycle) FOVs 2–5
K_a₁	W/K	1 × 10⁻⁶	1 × 10⁻⁶	Air conductance from cavity to FOV 1
K_a₂	W/K	1.5 × 10⁻⁵	1 × 10⁻⁵	Air conductance from cavity to FOV 2
K_a₃	W/K	10⁻³	10⁻³	Air conductance from cavity to FOV 3
K_a₄	W/K	5 × 10⁻³	2 × 10⁻³	Air conductance from cavity to FOV 4
K_a₅	W/K	10⁻⁵	0.5 × 10⁻⁵	Air conductance from cavity to FOV 5
F_c₁	—	8 × 10⁻²	5 × 10⁻⁴	View factor between cavity and FOV 1
F_c₂	—	0.923	6 × 10⁻⁵	View factor between cavity and FOV 2
F_c₃	—	0.704	5 × 10⁻²	View factor between cavity and FOV 3
F_c₄	—	0.8	0.08	View factor between cavity and FOV 4
F_c₅	—	0.2	0.02	View factor between cavity and FOV 5

Abstract

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Figures (7)

Tables (2)

Equations (19)

Applied Optics