Charles K. Gatebe, James J. Butler, John W. Cooper, Matthew Kowalewski, and Michael D. King, "Characterization of errors in the use of integrating-sphere systems in the calibration of scanning radiometers," Appl. Opt. 46, 7640-7651 (2007)
Laboratory measurements were performed to characterize the geometrical effects in the calibration of the NASA's cloud absorption radiometer (CAR). The measurements involved three integrating sphere sources (ISSs) operated at different light levels and experimental setups to determine radiance variability. The radiance gradients across the three ISS apertures were 0.2%–2.6% for different visible,
near-infrared, and shortwave infrared illumination levels but
in the UV. Change in radiance with distance was determined to be 2%–20%, being highest in the UV. Radiance variability due to the edge effects was found to be significant;
as much as 70% due to the sphere aperture and
due to the CAR telescope's secondary mirror.
Steven W. Brown, B. Carol Johnson, Stuart F. Biggar, Edward F. Zalewski, John Cooper, Pavel Hajek, Edward Hildum, Patrick Grant, Robert A. Barnes, and James J. Butler Appl. Opt. 44(30) 6426-6443 (2005)
B. C. Johnson, Giuseppe Zibordi, Steven W. Brown, Michael E. Feinholz, Mikhail G. Sorokin, Ilya Slutsker, John T. Woodward, and Howard W. Yoon Appl. Opt. 60(12) 3380-3392 (2021)
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Current Cloud Absorption Radiometer and ISS Specifications
Angular scan range
190°
Instantaneous field of view
17.5 mrad (1°)
Pixels per scan line
382
Scan rate
1.67 scan lines per second (100 rpm)
Spectral channels (μm; bandwidth (FWHM))
14a (Eight continuously sampled and last six in filter wheel): 0.340 (0.009), 0.381 (0.006), 0.472 (0.021), 0.682 (0.022), 0.870 (0.022), 1.036 (0.022), 1.219 (0.022), 1.273 (0.023), 1.556 (0.032), 1.656 (0.045), 1.737 (0.040), 2.103 (0.044), 2.205 (0.042), 2.302 (0.043)
Output channels
9 channels at 16 bits
Data rate
61.85 MBits h−1
Instrument mass
42 kg
Radiometric calibration
Spectral integrating sources:
Hardy: diameter 1.83 m (0.25 m)b range 0.4–2.3 μm; inside coating - BaSO4; Number of lamps: 16; 200 W∕lamp; 6.51 A; lamps∕PSUc 2; PSU model: HP 6554A; stability <0.05%.
Slick: diameter 1.22 m (0.25 m)b range 0.4–2.3 μm; inside - Spectralon® panels; Number of lamps: 16; 45 W∕lamp; 6.60 A; lamps∕PSUc: 4; PSU model: LPS-200-H (Labsphere); stability <0.03%.
Uncle: diameter 0.51 m (0.20 m)b range 0.23–0.40 μm; inside coating BaSO4; Number of lamps: 4; 150 W∕lamp; 6.00 A; lamps∕PSUc: 4; PSU model: ATE-100-100M (Kepco); stability <0.03%.
Spectral channels are named in the paper as channel 1, channel 2, … channel 14 following wavelength order as specified in this table.
Diameter of sphere exit aperture.
PSU - Power Supply Unit.
Table 2
Spatial Gradient of Radiance at Points-Across the Hardy Sphere Aperture (in percent)a
Channel
One Lamp
Two Lamps
Three Lamps
Four Lamps
Five Lamps
Six Lamps
12 Lamps
16 Lamps
1
10.71 ± 0.97
4.30 ± 0.51
3.38 ± 0.34
4.36 ± 0.30
4.21 ± 0.26
4.06 ± 0.21
3.09 ± 0.08
4.87 ± 0.05
2
14.59 ± 0.86
4.81 ± 0.45
4.34 ± 0.30
4.11 ± 0.26
3.37 ± 0.23
3.31 ± 0.18
2.81 ± 0.07
3.78 ± 0.04
3
1.57 ± 0.01
1.17 ± 0.00
1.24 ± 0.00
1.24 ± 0.00
1.29 ± 0.00
1.22 ± 0.00
1.25 ± 0.00
1.24 ± 0.00
4
1.21 ± 0.00
0.90 ± 0.00
0.97 ± 0.00
0.98 ± 0.00
1.01 ± 0.00
0.95 ± 0.00
0.97 ± 0.00
0.97 ± 0.00
5
1.21 ± 0.00
0.90 ± 0.00
0.96 ± 0.00
0.96 ± 0.00
1.01 ± 0.00
0.95 ± 0.00
Saturated
Saturated
6
1.18 ± 0.00
0.87 ± 0.00
0.93 ± 0.00
0.93 ± 0.00
0.98 ± 0.00
0.91 ± 0.00
Saturated
Saturated
7
1.05 ± 0.00
0.85 ± 0.00
0.91 ± 0.00
0.93 ± 0.00
0.98 ± 0.00
0.92 ± 0.00
1.01 ± 0.00
Saturated
8
1.24 ± 0.00
0.72 ± 0.00
0.75 ± 0.00
0.74 ± 0.00
0.78 ± 0.00
0.73 ± 0.00
Saturated
Saturated
The values are calculated from the difference between maximum and minimum radiance, normalized to the average radiance over all points across the Hardy sphere aperture at a given light level. The error is defined by the standard error (standard deviation∕square root of N; where N is the number of scans).
Table 3
Spatial Gradient of Radiance at Points Across Apertures of the Uncle Sphere and Slick Sphere (in percent)
The values are calculated from the difference between maximum and minimum radiance, normalized to the average radiance over all points across each ISS aperture at a specified light level. These gradients are for short distances from the ISS apertures. The gradients are higher especially in the UV for long distances. For example, at a distance of 274 cm from the Uncle sphere aperture, the gradients in channel 1 are: 4.81% (±0.26; 4-lamp level) and 6.72% (±0.25; 2-lamp level). Channel 2: 6.29% (±0.39; 4-lamp level) and 7.60% (±0.29; 2-lamp level).
Table 4
Difference Between Maximum Peak Radiance at Distance d1 and dN Relative to Radiance at d1 (Slick Sphere d1 = 23 cm and dN = 490 cm, and Uncle Sphere d1 = 30 cm, dN = 421 cm)a
Channel
Slick Sphere (%)
Uncle Sphere (%)
1
13.2(12.3)
2.0(6.1)
2
20.1(18.7)
5.1(8.4)
3
−6.5(−6.4)
Saturated (−6.1)
4
−5.9(−5.4)
−5.1(−5.1)
5
−6.5(−6.5)
Saturated
6
−7.2(−7.6)
Saturated
7
−8.9(−8.0)
Saturated
8
Saturated (−7.9)
Saturated
9
−9.0(−7.4)
No measurements
10
−8.8(−7.4)
No measurements
11
−8.8(−7.3)
No measurements
12
−8.2(−6.3)
No measurements
13
−7.7(−6.7)
−5.9(−6.3)
14
−7.1(−6.8)
No measurements
Values are for two light levels: Slick: eight-lamp level (four-lamp level); Uncle: four-lamp level (two-lamp level).
Table 5
Variation of Standard Deviation Peaks Relative to their Average Radiance as Function of Distance (%)
Values in brackets are for the inner peaks while the rest are for the outer peaks.
Tables (5)
Table 1
Current Cloud Absorption Radiometer and ISS Specifications
Angular scan range
190°
Instantaneous field of view
17.5 mrad (1°)
Pixels per scan line
382
Scan rate
1.67 scan lines per second (100 rpm)
Spectral channels (μm; bandwidth (FWHM))
14a (Eight continuously sampled and last six in filter wheel): 0.340 (0.009), 0.381 (0.006), 0.472 (0.021), 0.682 (0.022), 0.870 (0.022), 1.036 (0.022), 1.219 (0.022), 1.273 (0.023), 1.556 (0.032), 1.656 (0.045), 1.737 (0.040), 2.103 (0.044), 2.205 (0.042), 2.302 (0.043)
Output channels
9 channels at 16 bits
Data rate
61.85 MBits h−1
Instrument mass
42 kg
Radiometric calibration
Spectral integrating sources:
Hardy: diameter 1.83 m (0.25 m)b range 0.4–2.3 μm; inside coating - BaSO4; Number of lamps: 16; 200 W∕lamp; 6.51 A; lamps∕PSUc 2; PSU model: HP 6554A; stability <0.05%.
Slick: diameter 1.22 m (0.25 m)b range 0.4–2.3 μm; inside - Spectralon® panels; Number of lamps: 16; 45 W∕lamp; 6.60 A; lamps∕PSUc: 4; PSU model: LPS-200-H (Labsphere); stability <0.03%.
Uncle: diameter 0.51 m (0.20 m)b range 0.23–0.40 μm; inside coating BaSO4; Number of lamps: 4; 150 W∕lamp; 6.00 A; lamps∕PSUc: 4; PSU model: ATE-100-100M (Kepco); stability <0.03%.
Spectral channels are named in the paper as channel 1, channel 2, … channel 14 following wavelength order as specified in this table.
Diameter of sphere exit aperture.
PSU - Power Supply Unit.
Table 2
Spatial Gradient of Radiance at Points-Across the Hardy Sphere Aperture (in percent)a
Channel
One Lamp
Two Lamps
Three Lamps
Four Lamps
Five Lamps
Six Lamps
12 Lamps
16 Lamps
1
10.71 ± 0.97
4.30 ± 0.51
3.38 ± 0.34
4.36 ± 0.30
4.21 ± 0.26
4.06 ± 0.21
3.09 ± 0.08
4.87 ± 0.05
2
14.59 ± 0.86
4.81 ± 0.45
4.34 ± 0.30
4.11 ± 0.26
3.37 ± 0.23
3.31 ± 0.18
2.81 ± 0.07
3.78 ± 0.04
3
1.57 ± 0.01
1.17 ± 0.00
1.24 ± 0.00
1.24 ± 0.00
1.29 ± 0.00
1.22 ± 0.00
1.25 ± 0.00
1.24 ± 0.00
4
1.21 ± 0.00
0.90 ± 0.00
0.97 ± 0.00
0.98 ± 0.00
1.01 ± 0.00
0.95 ± 0.00
0.97 ± 0.00
0.97 ± 0.00
5
1.21 ± 0.00
0.90 ± 0.00
0.96 ± 0.00
0.96 ± 0.00
1.01 ± 0.00
0.95 ± 0.00
Saturated
Saturated
6
1.18 ± 0.00
0.87 ± 0.00
0.93 ± 0.00
0.93 ± 0.00
0.98 ± 0.00
0.91 ± 0.00
Saturated
Saturated
7
1.05 ± 0.00
0.85 ± 0.00
0.91 ± 0.00
0.93 ± 0.00
0.98 ± 0.00
0.92 ± 0.00
1.01 ± 0.00
Saturated
8
1.24 ± 0.00
0.72 ± 0.00
0.75 ± 0.00
0.74 ± 0.00
0.78 ± 0.00
0.73 ± 0.00
Saturated
Saturated
The values are calculated from the difference between maximum and minimum radiance, normalized to the average radiance over all points across the Hardy sphere aperture at a given light level. The error is defined by the standard error (standard deviation∕square root of N; where N is the number of scans).
Table 3
Spatial Gradient of Radiance at Points Across Apertures of the Uncle Sphere and Slick Sphere (in percent)
The values are calculated from the difference between maximum and minimum radiance, normalized to the average radiance over all points across each ISS aperture at a specified light level. These gradients are for short distances from the ISS apertures. The gradients are higher especially in the UV for long distances. For example, at a distance of 274 cm from the Uncle sphere aperture, the gradients in channel 1 are: 4.81% (±0.26; 4-lamp level) and 6.72% (±0.25; 2-lamp level). Channel 2: 6.29% (±0.39; 4-lamp level) and 7.60% (±0.29; 2-lamp level).
Table 4
Difference Between Maximum Peak Radiance at Distance d1 and dN Relative to Radiance at d1 (Slick Sphere d1 = 23 cm and dN = 490 cm, and Uncle Sphere d1 = 30 cm, dN = 421 cm)a
Channel
Slick Sphere (%)
Uncle Sphere (%)
1
13.2(12.3)
2.0(6.1)
2
20.1(18.7)
5.1(8.4)
3
−6.5(−6.4)
Saturated (−6.1)
4
−5.9(−5.4)
−5.1(−5.1)
5
−6.5(−6.5)
Saturated
6
−7.2(−7.6)
Saturated
7
−8.9(−8.0)
Saturated
8
Saturated (−7.9)
Saturated
9
−9.0(−7.4)
No measurements
10
−8.8(−7.4)
No measurements
11
−8.8(−7.3)
No measurements
12
−8.2(−6.3)
No measurements
13
−7.7(−6.7)
−5.9(−6.3)
14
−7.1(−6.8)
No measurements
Values are for two light levels: Slick: eight-lamp level (four-lamp level); Uncle: four-lamp level (two-lamp level).
Table 5
Variation of Standard Deviation Peaks Relative to their Average Radiance as Function of Distance (%)