UMAC Annual Meeting 2005

AgCam Calibration Test Results

Xiaodong Zhang

UMAC Annual Meeting 2005

Calibration Tests

• Spectral

• Radiometric

• Flat Field

• Focus

• Thermal Effects

• First light

UMAC Annual Meeting 2005

Spectral Calibration

LIGHT SOURCES

100W TungstenHalogenbulb

MONOCHROMETER

AgCam

M3

M2

M4M1

Spectral Calibration Configuration

CHOPPER

FILTER WHEEL

Collimator

Red Camera

NIR Camera

PDC

UMAC Annual Meeting 2005

Spectral Calibration – Quick Run

• Approximately determine the spectral band pass of the AgCam system

• Every 5 nm from 330 nm to 1200 nm

• 7 nm FWHM (bandwidth)• Integration time 400 s

for both cameras• Visually check if signal >

noise

UMAC Annual Meeting 2005

Quick Run – Results

• Spectral response 600 nm – 700 nm for the red camera and 780 nm – 900 nm for the NIR camera

• The responses of the AgCam optical system are below noise level for photons at wavelengths below 500 nm and above 950 nm

UMAC Annual Meeting 2005

Spectral Calibration – Slow Run• Every 2 nm from 550 – 750 nm for the Red and

from 750 – 950 nm for the NIR• Integration time 300 s for the Red and 400 s

for the NIR• 5 incident angles (far left, mid left, nadir, mid

right, far right)• Reference spectra taken before and after the run

for each angle• 50 seconds per wavelength x 200 wavelengths x

2 cameras x 5 angles = very very very slow!!!

UMAC Annual Meeting 2005

LIGHT SOURCES(Tungsten Lamp, Glowbar)

MONOCHROMETERMAS SPECTROMETER

M3

M2

M4M1

Spectral Calibration Configuration

CHOPPER

FILTER WHEEL

UMAC Annual Meeting 2005

Spectral Calibration – Preliminary Results

0

64

128

192

256

550 600 650 700 750

array low end

array center

array low mid

array high end

array high mid

0

64

128

192

256

750 800 850 900 950

Array center

Array low end

Array low mid

array high end

UMAC Annual Meeting 2005

500 550 600 650 700 750 800 850 900 950 10000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1System Transmittance

Wavelength (nm)

Tra

nsm

ittan

ce

Red

NIR

500 600 700 800 900 1000 1100 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Spectral Transmittance

Wavelength (nm)

Tra

nsm

ittan

ce

beamsplitter for red

beamsplitter for NIRred filter

NIR filter

UMAC Annual Meeting 2005

Spectral Calibration – preliminary conclusions

• Meets the requirement• Different spectral responses for different incident

angles (true for almost all flat filters, because travel distance of photons across the flat filter varies with incident angles)

• Non-symmetrical w.r.t. the optical axis (because long axis of the beam-splitter aligns with the CCD array

CCD Red

CCD NIR

Beamsplitter

UMAC Annual Meeting 2005

Spectral Calibration – to do• Correct for spectral

intensity of the incident light source

Relative Intensity vs. Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

550 600 650 700 750

Wavelength (nm)

Re

lati

ve

Inte

ns

ity

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Sili

co

n D

iod

e R

es

po

ns

ivit

y (

A/W

)

ref7.dat

ref8.dat

ref1.dat

ref2.dat

ref9.dat

ref10.dat

ref15.dat

ref16.dat

ref17.dat

ref18.dat

ref21.dat

ref22.dat

ref6.dat

Photodiode

Relative Intensity vs. Wavelength

0

0.2

0.4

0.6

0.8

1

1.2

750 850 950

Wavelength (nm)

Re

lati

ve

Inte

ns

ity

0

0.1

0.2

0.3

0.4

0.5

0.6

Sili

co

n D

iod

e R

es

po

ns

e (

A/W

) ref3.dat

ref4.dat

ref5.dat

ref11.dat

ref12.dat

ref13.dat

ref14.dat

ref19.dat

ref20.dat

Silicon Photodiode

UMAC Annual Meeting 2005

Radiometric Calibration

• Integrating sphere with 30” opening and 12 bulbs

• Due to saturation, only 6 bulbs were used

UMAC Annual Meeting 2005

Radiometric Calibration – Preliminary results and conclusions

Peak pixel value vs. #Bulbs

0

50

100

150

200

250

300

0 2 4 6 8

# Bulbs

Max

. pix

el v

alu

e

IR Camera

Red Camera

23

8

UMAC Annual Meeting 2005

Radiometric Calibration – Preliminary results and conclusions

CCD array center

Lens center

CCD center

Vignett effect, which need s to be corrrected

UMAC Annual Meeting 2005

Radiometric Calibration – to do

• Quantify the radiometric response in terms of radiance per digital count, using– Calibrated radiometric outputs of the

integrating sphere– Spectral responses of the AgCam system

• Pixel by pixel

UMAC Annual Meeting 2005

Thermal Effect• Temperature-

controllable chamber• Integrating

hemisphere with 20” opening

• T = 18C (site room temp), 30°C (normal temp at ISS), and 35°C (hot day at ISS)

UMAC Annual Meeting 2005

Thermal Effects – preliminary results

• The red camera is hotter than the NIR

• The camera temperatures are always ~10°C higher than ambient

• The camera temperatures increased rapidly during the 1st hour of operation (At the ambient temperature of 35C, they reached ~46C in about 50 minutes )

• At 18°C, the camera temperatures increased to 32°C during 4 hours.

Camera Temperature vs. Time

27.5

28

28.5

29

29.5

30

30.5

31

31.5

32

32.5

14:24:00 14:52:48 15:21:36 15:50:24 16:19:12 16:48:00 17:16:48 17:45:36 18:14:24 18:43:12

Time (HH:MM:SS)

Tem

per

atu

re (

C)

Camera 0

Camera 1

UMAC Annual Meeting 2005

Thermal Effects – Preliminary conclusions

• Don’t not operate the camera more than 1 hour.

UMAC Annual Meeting 2005

Taking Pictures

• AgCam mounted to 12” machine shop rotary indexing table

• Battery-operated drill drove the table at ~1 deg/s rotation of the camera

UMAC Annual Meeting 2005

UMAC Annual Meeting 2005