Precision Extended-Area Low Temperature

Precision Extended-Area Low Temperature Blackbody BB100-V1
for IR Calibrations in Medium Background Environment
S. Ogarev, M. Samoylov, V. Sapritsky, A. Panfilov
All Russian Research Institute for Optical and Physical Measurements (VNIIOFI), Moscow, Russia.
Suzuki Koichi, Takahiro Kawashima
NEC Toshiba Space Systems, Ltd., Tokyo, Japan
Abstract.
Paper reviews a new large-area
high-precision blackbody BB100-V1, designed at
the
All-Russian
Research
Institute
for
Opto-Physical Measurements (VNIIOFI, Russia) as
a source within 240 to 350 K temperature range for
preflight calibration of space-borne radiometric
instruments at such research organizations as
NEC TOSHIBA Space Systems and JAXA (Japan),
Keldysh Space Center (Russia). The temperature
non-uniformity and long-term stability account for
less than 0.1K and 0.1% for 1.5 μm to 15 μm
wavelength region under cryo-vacuum conditions
of medium background environment.
Introduction
The 10-year implementation plan for the GEOSS ( The
Global Earth Observation System of Systems) program
by representatives of more than 50 countries and more than
30 international organizations, besides the other tasks,
assumes development of optical instruments that can
measure radiance, reflective properties, and radiant
temperature of objects of observation [1]. Calibration of
IR sensors, thermal imagers, instrumentation for remote
earth sensing, signature recognition, and low background
spaceborne radiometers requires development of low- and
near-ambient-temperature reference standard sources
capable of operating in vacuum at low or medium
background conditions. The required accuracy and
long-term
stability
of
measurement
account
correspondingly for 0.1% and 0.02% per decade within the
0.2 to 3 μm spectral region; and 0.1K and 0.01K per
decade for 3 to 15 μm region. The most stringent
requirements for radiometric measurements come from
climatology, which requires decades-long high-quality
time series. The uniformity of those measurements should
be based upon uniform scales for the radiometric quantities
to be measured – spectral radiance and spectral irradiance.
The requirements can only be met if the ground calibration
is executed at a very high level of accuracy. As an
additional requirement, many applications require a
compact standard planckian source – blackbody (BB) for
near ambient temperatures operating both in vacuum and
in air with optional window and having high accuracy in
temperature setting.
In order to provide complete metrological support and
such precise pre-flight calibration of spaceborne
instruments, the development of precision BB sources of
radiation operating within VIS-IR wavelength ranges, like
BB100-V1, is of a great importance.
Blackbody BB100-V1 specifications
The blackbody BB100-V1 under consideration is
basically an extended area blackbody for low temperatures
(250 K up to 350 K), which operates under cryo-vacuum
conditions. The BB100-V1 was designed and
manufactured designed at the All-Russian Research
Institute for Opto-Physical Measurements (VNIIOFI,
Russia) for calibration of space-borne radiometric
instruments at NEC TOSHIBA Space Systems; JAXA
(Japan), and Keldysh Space Center (Russia). BB100-V1
specifications (obtained in tests) are presented in Table 1.
Table 1. BB100-V1 specifications
Parameter
Value
Operating temperature range
240 K - 350 K
1.5 μm – 15 μm
Spectral range
Cavity effective emissivity
Opening (non-precision aperture)
System Field-of-View (FOV)
Environment operation
conditions
Temperature non-uniformity
across opening
Temperature set point resolution
Maximum temperature instability
under thermostabilization
Limitation on the blackbody
warning-up time (approx.)
Total Wattage (approx.)
Input Voltage
Blackbody temperature set up
and control
Temperature sensors for control
system
Calibration traceability of Pt
RTD to NIST
Operating Environment Pressure
Orientation of the blackbody
Cable (tubing) length
0.997 ± 0.001
Ø100 mm
12 mrad (0.688º)
Vacuum chamber
(10-6 Torr, below 100 K)
Air environment
(clean room at 23 ± 3ºC)
0.1 K
0.01 K
0.05 K
2 hrs.
3500 W
(with usage of thermostat
LAUDA Proline PR1845)
100 V AC or 200 V AC
External controller with
RS-232 interface to
(optional) PC computer
Pt RTD, 5 pieces
(by MINCO Products, Inc.)
Yes, assumed for one
Pt RTD only
10-6 Torr
Facing down (±30º leaned)
5 m inside and outside
vacuum chamber
BB100-V1 prototypes and realization
In order to meet the requirements to accuracy and
long-term stability of measurements, the design of
BB100-V1 was based on the prototypes of high-precision
unique BBs developed within the last decade at VNIIOFI
[2,3]. Among them there are variable-temperature and
fixed-point models BB100, BB300, BB900, BB1000,
VTBB, BB29Ga, and BB156In with 100 K to 1000K
working temperature range, designed for calibration of
spaceborne IR sensors and high-precision radiometry at
such research organizations as German Aerospace Center
(DLR) and Physikalisch-Technische Bundesanstalt
(Germany), National Physical Laboratory (UK), Space
Dynamics Lab (USA), NIM and IAO (China).
Cavity-type BB100-V1 as a source of thermal radiation
features a series of advantages over any other thermal
sources – such as high reproducibility, low sensitivity of its
effective emissivity to variations and degradation of optical
properties of its cavity inner surface.
Low-temperature and cryogenic BB100-V1 is build up
on the principles of the usage of external liquid-based
thermostat LAUDA Proline PR1845-LCK1891 with
circulating coolant KRYO-51 in a closed loop.
As a material of radiating cavity for low-temperature
and cryogenic BB one can use copper and aluminum alloys.
The necessary value of emissivity was obtained with the
usage of black cover paints, e.g. Chemglaze Z-302 for
BB29gl blackbody or Nextel Velvet 811-21 for BB100 /
BB100-V1 radiation sources. While identifying
appropriate coating for BB-100V1 bottom possessing
emissivity better 0.9 in the spectral range of interest (see
Fig. 1), the Nextel Velvet Coating 811-21 was chosen by
ourselves after comparative analysis of several
comprehensive reviews [e.g., 4] on application and optical
properties of black paints and various coatings to stray
light suppressing, solar energy absorbing, for thermal
detectors of optical radiation, radiation losses control, etc.
0.990
0.985
0.980
0.975
Emissivity
0.970
0.965
0.960
0.955
[11]
0.945
[12]
0.940
0.935
0
1
2
Figure 2. BB100-V1 cross-section.
Cavity dimensions: 200 mm length x 120 mm diameter.
Table 2.
Normal Effective Emissivity of BB100-V1 Isothermal Cavity
Cavity Wall Diffusity
Cavity
Wall
0.7
0.8
0.9
1.0
Emissivity
0.935
0.9972
0.9976
0.9980
0.9983
0.990
0.9996
0.9996
0.9997
0.9997
The BB100-V1 is currently under testing in
cryo-vacuum chamber. The uncertainty of thermodynamic
temperature reproducibility of BB100-V1 within working
temperature ranges did not exceed 0,5K (1). The
temperature non-uniformity and long-term stability
account for less than 0.1K and 0.1% for 1.5 μm to 15 μm
wavelength region under cryo-vacuum conditions of
medium background environment. The results of these
measurements will be presented in the paper.
References
[10]
0.950
emissivity (0.935 and 0.990) and 4 values of wall diffusity.
The results of computations are presented in Table 2.
3
4
5
6
7
8
9
10
11
12
13
14
15
Wavelength (ì m)
Figure 1.
Spectral emissivity of Nextel Velvet Coating 811-21
It is enough to assume that the spectral hemispherical
emissivity of Nextel 811-21 is within 0.935…0.990
interval for wavelength range from 1.5 to 15 μm. The
measurements of reflectance performed for the predecessor
of Nextel 811-21, the 3M Velvet Black, show the presence
of a small specular component, less than 10% from overall
hemispherical reflectance; the diffuse component of
reflectance has the near-Lambertian BRDF.
The drawing of BB100-V1 design performed with the
account of above-mentioned studies is depicted in Fig. 2.
The computations of the normal effective emissivities
of an isothermal cavity depicted in Fig.2 using STEEP3 [5]
software. We have used the limiting values of wall
[1] V.I.Sapritsky, S.P.Morozova, B.E.Lisiansky, S.A.Ogarev,
M.K.Sakharov, M.L.Samoylov, A.S.Panfilov, B.B.Khlevnoy,
V.E.Privalsky The Global Earth Observation System of
Systems (GEOSS) and problems of measuring the radiant
properties of objects of observations . Proceedings of
NEWRAD’2005 (in print).
[2] V.I.Sapritsky, S.A.Ogarev, B.B. Khlevnoy, M.L.Samoylov,
V.B.Khromchenko “Blackbody sources for the range 100 K to
3500K for precision measurements in radiometry and
thermometry“ – in Proceedings of the 8th Symposium on
temperature: its measurement and control in science and
industry. Chicago, IL, U.S.A. October 21-24, 2002.
[3]
V.I.Sapritsky,
V.B.Khromchenko,
S.N.Mekhontsev,
M.L.Samoilov, A.V.Prokhorov, S.A.Ogarev, A.Shumway
“Medium Background Blackbody BB1000”. Conference CD
of CALCON’2000. SDL, Utah, USA, 2000.
[4] Hameury J, Hay B, Filtz J R 2003 Measurement of Infrared
Spectral Directional Hemispherical Reflectance and
Emissivity at BNM-LNE – Paper presented at the Fifteen
Symposium on Thermopysical Properties, June 22-27, 2003,
Boulder, CO, USA
[5] STEEP3, version 1.3. User’s Guide. Virial, Inc., NY, 2000