Transcript Slide 1

Sensitivity Calibration of Narrow Field of View
Optical Instruments
F. Sigernes 1, T. Svenøe 2, J. Holmes 1, M. Dyrland 1, D.A. Lorentzen 1,
J. Moen 3, 1, S. Chernouss 4, and C. S. Deehr 5
1
The University Center in Svalbard (UNIS), N-9171 Longyearbyen, Norway.
2 The Norwegian Polar Institute, Ny-Ålesund, Norway
3 Institute of Physics, University of Oslo, Norway
4 Polar Geophysical Institute, Apatity, Russia
5 Geophysical Institute, University of Alaska, Fairbanks, USA
BACKGROUND
The increasing number of low light level optical
instruments operated in Svalbard (Longyearbyen,
Barentsburg and Ny-Ålesund) for monitoring auroras
and airglow phenomena emphasizes the need for
establishing accurate calibration routines of international
standard.
CONTENT
1.
2.
3.
4.
THEORETICAL BASIS
EXPERIMENTAL SETUP AT UNIS
TRANSFER OF LAMP CERTIFICATE
SCREEN BRIGHTNESS CONTROL
1. THEORETICAL BASIS
a) Lambertian surface
b) Calibration setup
Irradiance certificate
4 zo Bo  4 z 2 Bz
2
 z o   # photons 
B z   B o    

2
 z   cm s Å 
2
Entering emission rate
 dA cos 
Rs d   Rs d 

z2


Reemitted radiation
 dA cos 
N   Rs d   
   R 0 d.
z2


Then
 R   dA cos 
R      s   
  cos.
z2

   
Lambert’s Cosine law
R 
 # photons
 R 0  cos , 

 s sr Å 
Radiance towards instrument becomes
 # photons


dA cos  s sr Å cm 2 
R   1 
    s    2   cos
   z 
Total hemispherical emission rate
L 
2 / 2
N 
  R d sin  d d .
0 0
 # photons
N    R 0 d. 

s


R
Since inverse square law is
Rs  Bz z 2  Bo zo
2
B  z 
L    0    0   cos
    z
The generalized Rayleigh
1R  1 / 4   10 # photons cm sec sr
6
2
1
Exitance of screen
1
 # photons
M    L . 

2
 cm s Å 
2
2. THE UNIS LABORATORY
(1) 18 x 18 inch2 Lambertian surface, (2) rails, (3) adjustable mobile table, (4) entrance fiber to spectrograph, (5) door with baffle, (6) room lights, (7)
tungsten lamp, (8) power cable to lamp filament.
2. THE UNIS LABORATORY
(A) THE FICS SPECTROGRAPH
(B) WAVELENGTH CALIBRATION
Low pressure mercury pen lamp
Mercury vapour tube
Fluorescent tube
  a0  a1  p  a2  p 2
Fixed Imaging Compact Spectrograph (FICS SN 7743): (A)
concave holographic grating, (B) flat mirror, (C) detector (CCD),
(D) fiber bundle, (E) entrance slit
Coefficients
Constants
a0
2.56026 x 10 +3
a1
7.99624 x 10
a2
1.95299 x 10 -4
Range 2560 – 10945 Å; FWHM ~ 80Å
0
3. RESULTS
TRANSFER OF LAMP CERTIFICATE
CERTIFIED 1000W TUNGSTEN
ORIEL SN7-1275 NIST TRACABLE
K 
M
C1000W
 # photons 
 cm 2 s Å cts 


SECONDARY STANDARD
200W TUNGSTEN (FRED01)
KEY PARAMETERS:
Exposure time 160 msec
z = 8.56 m
Filter: BK-7
FUNCTIONAL FIT (DOTTED LINE):

M 200W   5 exp a  b 1
a = 73.9 and b = 52568.

3. RESULTS
SCREEN BRIGHTNESS CONTROL
KEY PARAMETERS:
Secondary 200W Tungsten
Exposure time 160 msec
z = 8.56 m
Filter: BK-7
Distance increments = 0.5 m
4. CONCLUDING REMARKS
So far:
• The optical laboratory at UNIS is constructed according to basic
Lambertian theory to calibrate narrow field of view low light level
optical instruments.
• Secondary certification of a 200W Tungsten lamp has been
conducted in the visible part of the spectrum (4000 – 8000 Å).
• A procedure to control screen brightness without change in
spectral shape by varying the screen-lamp distance from 8 down
to 3.5m has been demonstrated in the 1 -132 kR/Å range of the
visible spectrum.
Future:
• A low power tungsten lamp is needed to calibrate below 1kR.
• Secondary certification above 8000 Å requires appropriate cutoff filters.
• A new monochromatic is installed and ready for use as source to
calibrate filters instruments.
• …