Download 4. in-flight calibration plan

Laboratory for Atmospheric & Space Physics
University of Colorado
Boulder, Colorado
INSTRUMENT CALIBRATION PLAN
Cloud Imaging and Particle Size Experiment
(CIPS)
on the
Aeronomy of Ice in the Mesosphere (AIM) Mission
LASP/CU Document Number:
Prepared by: Bill McClintock
VER
A
DESCRIPTION OF CHANGE
Initial Release
Date:
DR
APPVD
DATE
Cloud Imaging and Particle Size Experiment
TABLE OF CONTENTS
1.
CIPS INVESTIGATION...................................................................................................... 3
1.1 PMC MORPHOLOGY AND GRAVITY WAVES ............................................. 3
1.2 CLOUD PARTICLE SIZE, MASS, AND SURFACE AREA .............................. 4
N/A.................................................................................................................................. 5
N/A.................................................................................................................................. 5
2. CIPS INSTRUMENT OVERVIEW ...................................................................................... 6
3. PRE-FLIGHT CALIBRATION PLAN ................................................................................... 9
3.1 UNIT LEVEL....................................................................................................... 11
3.2 SYSTEM LEVEL ................................................................................................ 11
4. IN-FLIGHT CALIBRATION PLAN ..................................................................................... 1
4.1 STAR CALIBRATION ................... ERROR! BOOKMARK NOT DEFINED.
4.2 IN-FLIGHT FLAT ........................... ERROR! BOOKMARK NOT DEFINED.
5. RADIANCE/REFLECTANCE DETERMINATION AND ERROR ANALYSIS ............... 1
5.1 RADIANCE CONVERSION ............................................................................... 1
5.2 ERROR ANALYSIS................................................................................................. 2
6. REFERENCES ...................................................................................................................... 2
Instrument Calibration Plan (ICP)
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Cloud Imaging and Particle Size Experiment
CIPS Instrument Calibration Plan (ICP)
1. CIPS INVESTIGATION
The Cloud Imaging and Particle Size (CIPS) instrument is a panoramic UV (265 nm) imager
that will view in the nadir direction and will image the polar atmosphere at over a range of angles
in order to determine Polar Mesospheric Cloud (PMC) presence, measure their spatial
morphology and constrain the parameters of their particle distribution. CIPS will provide:

Panoramic nadir imaging with a 120º x 80º field-of-view (1140 x 960 km),

Scattered radiances from Polar Mesospheric Clouds near 83 km altitude, which will be
used to derive PMC morphology and constrain cloud particle size information,

Rayleigh scattering radiances from the background near 50 km altitude, which measure
gravity wave activity,

Multiple exposures of individual cloud elements that measure scattering phase function
and detect spatial scales to approximately 2 km, and

Measurements in the ultraviolet band pass (265 ± 7 nm) which maximize cloud contrast.
During each orbit CIPS will acquire a contiguous set of 34 panoramic images spaced
approximately 300 km apart (~ 43 second imaging cadence) from 50˚ latitude and extending 90˚
across the summer pole and into shadow.
1.1
PMC MORPHOLOGY AND GRAVITY WAVES
PMCs are identified in nadir images as small enhancements of brightness against the
Rayleigh-scattered background coming from the lower atmosphere. To minimize the background
intensity, CIPS employs an interference filter, which is centered on the spectral “hole” produced
by atmospheric ozone. Thomas et al. (1991) proved the feasibility of this detection method using
273.5 nm data from the SBUV nadir-viewing spectrometer on board of NIMBUS 7. They
showed that the brighter PMCs could be distinguished against the background, despite underfilling the 750 x 750 km FOV.
For observations with solar zenith angles from 87 deg to about 94 deg (the shadow band), the
PMCs remain in sunlight while the Rayleigh-scattering atmosphere is in shadow. This viewing
geometry reduces the background signal by a factor of 10 or more. Since the PMCs remain at
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Cloud Imaging and Particle Size Experiment
least 95% illuminated relative to an overhead sun condition their contrast is greatly enhanced.
CIPS will observe scenes with and without clouds in high and low background and will track
clouds into and out of the low background regions.
Although most of the AIM science objectives can be accomplished with measurements in the
low-background shadow band, CIPS is also capable of observing at higher Sun conditions where
gravity wave signals in the background will be emphasized. Gravity wave effects on CIPS
signals come from the dependence of O3 photochemistry on temperature. Waves as small as 1-2
K at 50 km will cause a 3% perturbation in background signal, which will be detected by CIPS.
CIPS supports two additional methods for identifying PMCs and distinguishing against
spatial variations in the background. The first relies upon the Mie scattering-angle signature of
PMCs. Brightness enhancements that show forward scattering behavior (more pronounced for
brighter clouds, or more specifically clouds having larger particle size,) can be identified as
PMCs, and not an underlying background irregularity (which would obey the well-known
symmetric Rayleigh scattering phase function). A second method relies on the different apparent
drifts over the six-cloud sequence of PMC at 83 km and the lower-lying background patterns
originating near 60 km. This leads to a methodology for separation of the gravity wave signature
on the cloud albedo from that of the underlying background
1.2
CLOUD PARTICLE SIZE, MASS, AND SURFACE AREA
CIPS measurements will constrain the particle size distribution, f(r), at multiple locations
along the thin flat layers of PMCs. This analysis will concentrate on the common volumes, in
low background, also observed by SOFIE (i.e. the volume centered on the terminator that
contains clouds along the line of sight from the spacecraft to the sun as seen just after sunrise at
83 km). The f(r) function is critical for the determination of column mass and surface area,
quantities that are needed for study of the cloud microphysics and surface-induced heterogeneous
chemistry. The method, which uses the cloud particle’s scattering-angle signature, will be
applied to the brighter clouds that (1) exhibit forward scattering behavior, (2) appear in at least
four successive images and (3) lie significantly above the noise level. For this class of PMC it
will be possible to derive the particle concentration, the mean particle size, and the width of the
size distribution, assuming the width parameter of the log-normal size distribution (Thomas and
McKay, 1985). Thus, given the water-ice composition (verifiable from SOFIE IR extinction
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Cloud Imaging and Particle Size Experiment
versus wavelength measurements), the combination of cloud radiances along with least-squares
analysis of CIPS angular distributions at a single wavelength will yield column mass and surface
area.
This will allow correlation of PMC size with PMC extinction, T, H2O and other
atmospheric parameters.
Given S/C pointing capabilities, image resolution, and the typical large horizontal extent of
thin-layered PMCs, it will be possible to identify distinct clouds or cloud features in successive
images (43 sec apart). Cloud lifetimes are of the order of hours to several days (Thomas, 1991).
It is known that the small-scale (5-10 km) “billows” have a lifetime of about 5 minutes, and
appear to track the mean wind (Witt, 1962). The important point for CIPS is that gravity waves
are limited to periods larger than about 5 min. near 83 km. Furthermore, these high-frequency
waves are minor contributors to the T variance, compared to the longer-period waves responsible
for the prominent “bands” that occur in ground based images of PMCs. In effect, successive
images by CIPS on a given overpass will “freeze” all but the most rapidly varying waves, which
have little effect on the environment of PMCs, such as T and H2O. The detailed dependence of
the gravity wave-induced structure of PMCs on these variables will be defined at the low
background points of intersection of the SOFIE and CIPS fields of regard.
Table 1 summarizes the measurement requirements for the CIPS investigation.
Table 1. CIPS Measurement Requirements
Geophysical
Parameter
PMC Presence
PMC Morphology
PMC Particle Size
Observable
Scattered
Sunlight @
@ 265 nm 
7 nm
Ratio:
Cloud to
Background
Inferred
Gravity
Wave Effects
Horizontal
Resolution
50 (10) km
Instrument Requirement (Goal)
Expected Performance (PDR)
Absolute
Precision (SNR)
Accuracy
SNR=2 for AR=11 (AR=2)*
N/A
2 km
SNR=6.5 for AR=2 and R=2 km
50 (10) km
15%
SNR=20 for AR=5 (AR=2)
2 km
10%
SNR=19.6 for AR=2 and R=5 km
200 (50) km
50%
SNR=10 for AR=5 (AR=2)
5 km
10%
SNR=13.4 for AR=2 and R=3 km
3 (2) km
N/A
SNR=10 (20) for AR=11
2 km
SNR=32.1 for AR=11 and R=2 km

PMC Presence Precision: Requirement-2-sigma detection clouds with Albedo=10-4 in the
common volume where the clear Albedo=10-5 (AR=11). Goal-2-sigma detection clouds with
A=10-5 against an A=10-5 background (AR=2)
Albedo Ratio=(Cloud Albedo +Background Albedo)/Background Albedo
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Cloud Imaging and Particle Size Experiment
2. CIPS INSTRUMENT OVERVIEW
The CIPS instrument consists of 4 wide-angle cameras, each with a 44˚ x 44˚ square field of
view, mounted in a cruciform configuration. Forward and aft cameras have their boresights
located ± 40˚ from the sub-spacecraft point. The nadir cameras have their boresights located ±
20˚ from the sub-spacecraft point in a plane orthogonal to the forward and aft cameras, producing
the instrument footprint shown in Figure 1.
Figure 1. CIPS instrument footprint
Each camera (See Figure 2) consists of an F/4, lens system with a 24.85 mm effective focal
length followed by a narrow band interference filter and intensified CCD detector.
The
interference filter limits the instrument sensitivity to a narrow wavelength range centered at 265
nm allowing CIPS to detect reflected light from faint PMCs, located at an altitude of ~83 km,
against a dark background created by ozone absorption, which peaks at ~ 40 km. Cloud albedos
in the CIPS wavelength range are typically 10-5 to 10-4 corresponding radiance values are 65 to
650 kRayleighs when integrated over the ~15 nm bandpass of the filter. Both the clouds and the
residual background from the atmosphere above 50 km (referred to as the Rayleigh scattered
background) are polarized.
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Cloud Imaging and Particle Size Experiment
Figure 2. CIPS camera head
The intensifier uses a semi-transparent cesium telluride (CsTe) photocathode, deposited on
the inner surface of a fused silica input window, to convert incident ultraviolet photons into
electrons. Photoelectrons from the cathode are proximity-focused onto the input of a single
microchannel plate (MCP) by accelerating them through a 50 volt potential. The MCP, which
has 0.01 mm diameter micro-pores, amplifies the single input electron, producing a localized
packet of electrons that is accelerated through a ~6000 volt potential onto a phosphor coated
output window producing a ‘pulse’ of visible light. The typical spatial extend for a phosphor
light pulse is ~ 0.02 mm FWHM, limiting the intensifier resolution to approximately 25 linepairs per mm. For CIPS the intensifier is equipped with a P-43 phosphor, which peaks at a
wavelength of ~545 nm and decays in intensity by a factor of 103 within 0.01 seconds after each
pulse. The voltage between the photocathode and MCP can be gated on or off, acting as an
electronic shutter for the system.
CsTe was chosen as the photocathode material because it provides additional rejection for
visible light from the lower atmosphere. The combination of filter and phtotcathode are designed
to limit signals from visible light to less than 10% of the weakest expected cloud, which is
equivalent to the signal detected from a 6.5 kRayleigh source emitting in the CIPS bandpass.
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Cloud Imaging and Particle Size Experiment
The CCDs have a 2048x2048 format with 0.014 mm square pixels. These are binned 4x4 to
produce a minimum 0.056 mm square detector resolution element, or ‘science pixel’ with a 2.25
mrad field of view. Only a 335 x 335 (1340 x 1340 unbinned) sub-array of pixels, corresponding
to 44˚ x 44˚ are telemetered in flight. The corner of the sub-array can be specified by ground
command, allowing on-orbit adjustment of the relative fields of view of the four cameras to
provide 2˚ overlaps at each camera pair boundary (Adjacent cameras each view a common 2˚
strip). Thirty-two lines of Time Delayed Integration (TDI) are used in the nadir cameras to
increase the effective image capture time to 1.29 seconds. (Nominal spacecraft motion results in
an apparent cloud speed 14 mrad per second equal to about 24.9 CCD rows per second.) The
rapidly changing footprint scale of the fore and aft cameras (See Figure 1) preclude the use of
TDI and their integration times are set to produce a 5km image smear at camera center (t~ 0.71
sec), which is comparable to the projected science pixel footprint.
Estimated instrument optical throughput, which is determined by lens transmission (0.9 to 0.7
from center to edge respectively), filter transmission (0.3), intensifier quantum efficiency (0.08),
and viewing geometry (cos()4, where  is the field angle measured from camera center), varies
from ~2% to ~1% across a camera FOV( 0˚ to 30˚ from center to corner)). When this is coupled
with the etendue of a single 0.056 mm square science pixel (1.54 x 10-6 cm2-str), the instrument
sensitivity is ~ 3.3 x 10-8 on axis and ~1.45 x 10-8 at a 30˚ field point. Thus, a 65 kRayleigh
signal (radiance for a 10-5 cloud albedo) produces ~ 170 photo events in 1 second on axis and ~85
events per second in the corners. Intensifier excess noise adds a factor of two to signal variance
caused by photon noise alone implying that the current best estimate for camera signal-to-noise is
given by:
S  2.66  kR t and
SNR  1.33  kR  t (center)
S  1.16  kR t and
SNR  0.58  kR  t (edge)
where kR is the radiance in kRayleighs and t is the integration time. These estimates, which are
uncertain by a factor
 of ~30%, will be updated with measured values during camera level
calibrations to meet the PMC morphology measurements requirements, which set a 10%
accuracy goal for determining the instrument radiometric sensitivity (Table 1).
CIPS cameras are protected from direct solar illumination by baffle systems that are tailored
to the individual cameras. The forward camera is most sensitive to contamination by scattered
sunlight because its FOV comes within 14˚ of the sun at first light. Furthermore, the sun is not
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Cloud Imaging and Particle Size Experiment
always in the plane of the spacecraft and it is necessary to yaw up 9˚ and roll up to 35˚ in order
that CIPS can observe the terminator at the correct latitude and longitude. The baffle systems are
required to reduce any signal from direct solar illumination or from sun light scattered spacecraft
surfaces to less than 10% of a PMC with 10-5 albedo for all AIM mission observational
geometries.
A bright object sensor (BOS), mounted on and co-boresighted with each camera with an
accuracy of 1˚, protects it from direct solar illumination. In contrast to the baffles, which are
designed so that CIPS can operate close to the sun, the BOS is designed to safe its camera by
turning off the high voltage power supply, if the sun enters the 50˚ x 50˚ FOV of the BOS.
The CIPS instrument performance parameters are summarized in Table 2.
Table 2. CIPS Performance Requirements
Parameter
Value
Wavelength Range
265 ± 7 nm
Instrument Field of View
80˚ cross track x 120˚ along track
Camera Field of View
44˚ x 44˚
Angular Resolution
2.25 mrad per 0.056 mm pixel
Sensitivity
SNR=10 a=10-4 and AR=11
Sensitivity Knowledge
10% goal, 15% required
Out of Band Signal
< 10% of a cloud with A=10-5
Scattered Sunlight
< 10% of a cloud with A=10-5
Camera-to-Camera Alignment
±1˚ per camera (0.25˚ knowledge)
Camera-to-BOS Alignment
±1˚ (0.5˚ knowledge)
3. PRE-FLIGHT CALIBRATION PLAN
CIPS pre-flight calibrations are designed to accurately measure the instrument performance
and to verify it meets its requirements. A mapping of performance requirement to specific
calibration/test is summarized in Table 3.
They include both unit level and system level
measurements. Component vendors will perform unit level tests for some optical and detector
elements (lens transmission, filter transmission and out-of-band rejection, CCD characteristics)
Table 3. Performance Requirements and Calibration/Characterization Summary
Performance Requirement
Wavelength Range: 265± 7 nm.
operational temperature range.
Measure over
Instrument Calibration Plan (ICP)
Calibration / Test
Manufacture’s certification. Check in CTE2 using D2 lamp
and PMT.
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Cloud Imaging and Particle Size Experiment
Out of Band Rejection: Better than 1% of in-band
response. Test filters for pinhole leaks.
Focus Adjust: within ± 0.05 mm
Camera Point Spread Function: 60% encircled
energy within 0.056 mm square pixel.
Camera Boresight: Measure relative to mounting
feet. Knowledge to 0.06˚ (0.5 pixels)
Camera Field of View: 44˚ Square. Measure to
0.06˚ (0.5 pixels)
Camera-to-Camera FOV Overlap: 2˚. Measure to
0.06˚ (0.5 pixels)
Camera Distortion; Determine distortion to 1% over
the field
Camera Polarization: < 10% with 5% relative
accuracy.
Camera Baffle Light Rejection: 2x10-6 when the sun
comes within 5˚ of the line of sight.
Camera Off-axis response: 2 x10-3 at 75˙ with light
illuminating the lens.
Camera Radiometric Sensitivity:
Measure over
operational temperature range with an absolute
accuracy of 15%.
Determine relative responsivity as a function of
angle to 2%.
Measure quasi-monochromatic response at 5
wavelengths and the 9 Zygo field points.
Detector characteristics: Measure over operational
temperature range.
CCD Read noise: 10% accuracy
CCD Dark current, flat field, and noise: 10%
accuracy
CCD Linearity: to 95% full well at with 2% accuracy
CCD Flat field: 1% accuracy
Intensifier Linearity: 5% accuracy
Intensifier quantum efficiency and excess noise
Relative temperature sensitivity 2% per ˚C accuracy
Instrument light leaks: <10%detector dark rate
Bright Object Sensor FOV: 50˚ Square Measure to
±0.5˚
Boresight with Camera to ±1.0˚
Bright Object Sensor Discriminator Level: 25%
absolute accuracy. Provide factor of 2 margin in
range.
Time Delayed Integration
Manufacturer’s certification for filter response modeled with
the instrument visible light response. Check filters for
pinhole leaks using sunlight from heliostat.
Use 45 cm collimator and star simulator. Fill telescope
aperture. Requires 2-axis manipulator. Check focus at 9
points in the FOV.
Camera head focus test with flight detector. Use 45 cm
collimator, star simulator, and 2-axis manipulator. Measure
at 9 points in the FOV. Document focus.
Use 45 cm collimator and star simulator. Fill telescope
aperture.
Requires
2-axis
manipulator.
Equal
measurement accuracy is required for alignment cube to
spacecraft.
Field of view map. Use 45 cm collimator, star simulator,
and 2-axis manipulator.
Use star source and AFTP. Measure 3 cameras at one
time.
Measure grid pattern. Use a 16 x 16 matrix with 1” bars
spaced 6” on centers located at a distance of 10’
Use 45 cm collimator, polarizer, and star simulator. Fill
telescope aperture.
Measure using deuterium lamp, collimator and 265 nm uv
filters in front of PMTs. Place one PMT in direct beam
path. Place second near the rear of the forward camera
aperture.
Use 45 cm collimator, star simulator, and 2-axis
manipulator. Fill telescope aperture.
Use NIST-calibrated irradiance lamps (D2 and FEL) and
white reflectance screen. Sensitivity measurements must
be corrected for scattered light, dark current/count,
linearity, and field of view variations. Measure
monochromatic response in CTE II (check polarization).
Integrate wavelength response to compare with lamp
spectral irradiance.
Measure before installation in the flight instrument. Verify
dark count and temperature coefficients during instrument
system test and qualification (thermal vacuum tests).
Cover aperture and illuminate instrument with sunlight
using heliostat.
Use 45 cm collimator, star simulator, and 2-axis
manipulator to measure BOS FOV and to check coalignment.
Set discriminator level using solar illumination from
heliostat and a transfer diode that views the sun directly.
Test 32 and 64 lines for both A and B readout chains
before delivery. Detailed detector unit level characterization and CIPS system level
characterization/ calibration will occur in the LASP/CU calibration laboratory. Additional CIPS
system level calibration verification will take place at OSC as schedule permits.
Instrument Calibration Plan (ICP)
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Cloud Imaging and Particle Size Experiment
3.1
UNIT LEVEL
Optical Components: Unit level measurements of optical components supplied are used for
screening and selection of individual components. Measurements of witness slide reflectivities
will be returned with lenses as they are coated. We have received efficiency curves from the
coating vendor, measured for S and P polarizations, as well as transmission and out-of-band
rejection curves for the interference filters. The filters will also be checked for pinhole leaks
before installation in flight camera assemblies.
Detectors: The intensifier will undergo a rigorous test program. All candidate intensifiers are
initially screened for quantum efficiency, dark current, photocathode uniformity, and gain versus
high voltage. These characteristics are remeasured after final detector head assembly. The flight
detector assemblies (assembled intensifiers, CCD and drive electronics, high voltage power
supplies, and interface electronics) will be characterized before being installed in its camera
housing. Measurements include quantum efficiency, photocathode field of view maps, dark
signal as a function of temperature, gain, linearity, and excess noise. CCDs will be characterized
for DC offset, dark current, dark current drift (at fixed temperature), pixel-to-pixel uniformity
(both dark current and sensitivity), linearity, and photon transfer. Flight detectors will be
selected for best pixel-to-pixel uniformity and lowest dark current. Dark current and flat field
tests will be repeated for the flight detector heads (detectors +electronics) before instrument
installation. Linearity will be determined by collecting a series of flat fields as a function of time.
Overall detector linearity will be determined by measuring detector response (DN per input
photons) as a function of high voltage using a fixed input light level. A family of curves will be
constructed by varying the input light level for each detector run. Intensifier quantum efficiency,
excess noise, and gain are measured by calculating the intensities of individual photo-events
during low light level illumination.
Camera Heads: Individual camera head characterizations and calibrations include imaging,
relative sensitivity, and polarization as a function of field angle. Absolute sensitivity will be
measured at field of view center. The imaging performance of at least one camera (most likely
the engineering model) will be tested over the full operating temperature range.
3.2
SYSTEM LEVEL
Instrument functional tests precede calibration. These verify proper function of operational
modes, search for detector cross talk, and electrical interference. In some cases correct function
can only be completely verified during system calibration when the instrument is stimulated by a
known source. Examples include data compression algorithms and detector cross talk. The
Instrument Calibration Plan (ICP)
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Cloud Imaging and Particle Size Experiment
instrument will also be checked for light leaks during functional testing by illuminating it with
sunlight through the heliostat located in the LASP optics laboratory. Leaks resulting in detector
output greater than 10% of the dark current will be sealed before the formal instrument
characterization/calibration.
The system level calibrations for the CIPS include imaging, field of view, scattered light,
photometric sensitivity, and camera scattered light and pointing characteristics of assembled
instrument. Accurate radiometric calibration requires that the instrument full aperture be filled.
This can be accomplished by illuminating a white reflectance screen or a diffuser screen placed at
the focus of the collimator telescope. Field of view maps require a filled telescope aperture from
a star source and a precision gimbal for rotating the CIPS instrument in two axes.
Individual camera head boresight will be measured using a star simulator and a precision 2axis instrument gimbol. The relative position of the camera boresight with respect to the
alignment cube and with respect to the instrument mounting feet depend on both CIPS platform
distortion and the motion of the camera optics in their mechanical mountings. The in-flight
boresight of CIPS relative to spacecraft star trackers will be measured by observing stars.
CIPS radiometric calibration is based on observations of white reflectance screens (Grum et
al.) that are illuminated by NIST-calibrated irradiance lamps to produce a radiance standard for
200 nm that fill the instrument aperture and field of view. Both deuterium lamps (200<<320
nm) and FEL lamps (>250 nm) will be used for these measurements. Screen measurements
must be combined with quasi-monochromatic relative sensitivity measurements across the ~ 15
nm CIPS bandpass using CTE II. At least the engineering camera and one flight camera should
be measured at the 9 field points used in the lens focus tests performed at Zygo. Check CIPS
polarization first because CTE II is polarized and two orthogonal measurements at each field
point may be required. Sensitivity measurements must be corrected for scattered light and dark
current linearity.
Point spread function, relative radiometric response, detector dark current and dark current
drift, and telescope boresight will be measured over the CIPS orbital operational temperature
range using the temperature controller in the BEMCO.
Table 4 summarizes the facilities required to execute the preflight calibrations and the
anticipated accuracy of the results. All of these facilities are dedicated to CIPS during its entire
qualification and calibration schedule.
Table 4. Requirements, Anticipated Ground Results, and Calibration Facilities
Performance Requirement
Wavelength Range: 265± 7 nm.
Measure over operational temperature
Instrument Calibration Plan (ICP)
Ground Test
± 0.1 nm
Facilities
Measurements
verifications
provided
by
Barr
Inc
and
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Cloud Imaging and Particle Size Experiment
range.
Out of Band Rejection: Less than 1%
of in-band response.
Focus Adjust:
Camera Point Spread Function: 60%
encircled energy within 0.056 mm
square
pixel.
Measure
over
temperature.
Camera Boresight: Measure relative to
mounting feet. Knowledge to 0.06˚
Camera Field of View: 44˚ Square.
Measure to 0.06˚
Camera-to-Camera FOV Overlap: 2˚.
Measure to 0.06˚
Camera
Distortion;
Determine
distortion to 1% over the field
Camera Polarization:
Factor of
minimum
margin
± 0.05 mm
2
Measure
radius
to
within 10%.
0.06˚ = ± 0.5
pixels
0.06˚ = ± 0.5
pixels
0.06˚ = ± 0.5
pixels
1% = ± 1.5
pixels at the
FOV edge.
< 10% with
±5% relative
accuracy.
Camera Baffle Light Rejection: 2x10-6
when the sun is within 5˚ of the line of
sight.
Camera Off-axis response: 2 x10-3 at
75˙ with light illuminating the lens.
Camera
Radiometric
Sensitivity:
Measure over operational temperature
range with an absolute accuracy of
10%.
Determine relative responsivity as a
function of angle to 2%.
Measure
quasi-monochromatic
response at 5 wavelengths and the 9
Zygo field points.
Detector characteristics:
Measure
over operational temperature range.
Read noise: 10% accuracy.
Dark
current, flat field, and noise: 10%
accuracy. CCD Linearity: to 95% full
well with 2% accuracy. CCD Flat field:
1% accuracy. Intensifier Linearity:
measure with 5% accuracy. Intensifier
quantum efficiency and excess noise:
25% accuracy. Relative temperature
sensitivity: to 2% per ˚C (gain)
Instrument light leaks: <10% dark rate
Bright Object Sensor FOV: 52˚ Square
Measure to ±0.5˚
Boresight with Camera to ±1.0˚
Bright Object Sensor Discriminator
Level:
25%
absolute
accuracy.
Provide factor of 2 margin in range.
Measurements provided by Barr Inc. and Hamamatsu.
Combine with instrument sensitivity model.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator.
D2 lamp.
Check temperature
dependence in BEMCO tank.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp.
Distortion target and FEL lamp. Temperature dependence
measured using MASCS/MOBY temperature controller.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp. UV polarizer. Rotate camera.
Measure before installation in the flight instrument.
Collimator, dedicated PMTs and filters, welding room.
Optics laboratory. 45 cm collimator, star simulator, and 2axis manipulator. D2 lamp.
Use NIST-calibrated irradiance lamps (D2 and FEL) and
white reflectance screen. Sensitivity measurements must
be corrected for scattered light, dark current/count,
linearity, and field of view variations. Measure
monochromatic response in CTE II (check polarization).
Integrate wavelength response with lamp spectral
irradiance. Screen size should be ~5˚ to 10˚ square as
seen by the instrument. Temperature dependence
measured using MASCS/MOBY or BEMCO temperature
controller.
Measure CCD read noise, dark current, photon transfer,
and photon transfer/w binning, windowing, and TDI with
flight electronics stack in thermal oven.
Measure assembled detector characteristics in CTE II.
Include flat field, linearity, and relative temperature
sensitivity.
FOV to 0.5˚
relative
to
mount.
25% absolute
accuracy.
Direct solar illumination with heliostat
Use collimator with 0.5˚ source and 2-axis manipulator.
Calibrate engineering detector against sun. Transfer to
flight units in the lab
The instrument command and data interface computer uses the OASIS software package and
is linked to a data computer in order to provide near real-time display of both engineering and
science data. Software necessary to perform ‘quick look’ analysis and validation of both
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Cloud Imaging and Particle Size Experiment
qualification and calibration data will be tested during instrument development using the
instrument engineering model.
Unit level calibrations and system characterizations (eg. Stray and scattered light, telescope
off-axis light, polarization, and point spread function) will be measured once, before instrument
environmental test. Key system level calibrations, telescope boresight, radiometric sensitivity, ,
will be performed before and after instrument environmental test. Table 5 summarizes the CIPS
calibration activities for performing calibration measurements during ground test and in flight
(See below).
Instrument Calibration Plan (ICP)
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Table 5. Pre and Post Launch Calibration Activities
Function
Parameter
Notes
Stray and
Scattered
Light
Telescope Off-axis Light
Measure over ~ 2Check edge for
Instrument level to verify solar rejection
Front baffle for solar rejection. Other baffles
for line of sight.
Wavelength
Range and
Out of Band
rejection
Imaging
Characteristics
Baffle functionality
Light leaks
Barr data sheets
Quick verification
Pinhole leaks
Focus
PSF
Distortion
Field of view/boresight
Alignment
Polarization
Center of camera
relative to reference
cube
Camera overlap regions
Known as a function of temperature??
Use 502 to check band.
Flood with out of band light
Detector
Camera
X
X
X
X
X
X
X
X
X
Use 18” collimator. Shim to focus
Image at selected points in an ‘X’ pattern.
Spot check at instrument level 6.25 meters
gives 0.1 mm defocus.
Instrument
X
X
X
X
X
X
X
X
fov edges relative to the camera mounting
surface
Measure over the field
Relative over field
Center of field
Dark/Dark FF over
temperature
Dark Noise over
temperature
Read Noise
Bias over temperature
Flat Field over
temperature
Relative sensitivity over
temperature
Non linearity
Intensifier saturation
Flight
X
X
X
pre/post
environment
X
pre/post
environment
X
X
X
X
X
Camera relative to s/c
TDI Image
Test
Radiometric
Sensitivity
Detector Tests
Post S/C
E.T.
Test nadir cameras only
X
X
Instrument level during thermal vacuum test
X
X
X
X
X
X
X
X
X
X
X
Instrument level during thermal vacuum test
X
X
X
X
X
Instrument level during thermal vacuum test
Instrument level during thermal vacuum test
Instrument level during thermal vacuum test
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Detector head level
Detector head level
X
X
X
X
4. IN-FLIGHT CALIBRATION PLAN
The in-flight calibration plan for the CIPS include observations of bright O-B stars (radiometric
sensitivity, field of view, and telescope boresight, relative to spaceraft nadir) and measurements
of the cloud-free Raleigh scattered background (flat field sensitivity and dark current).
Observations of bright O-B stars provide validation and tracking for pre-flight radiometric
sensitivity, point spread function, and boresight. Table 6 lists stars observed by the SOL STellar
Irradiance Comparison Experiment aboard both the UARS and SORCE satellites. These stars all
provide sufficient flux to provide an absolute radiometric calibration for CIPS accurate to ~ 10%.
The boresights for the individual CIPS cameras relative to each other and relative to the
spacecraft star tracker will be established with star field images.
Table 6. CIPS Calibration Stars
Star
a Cma
RA (2000)
Dec (2000)
Sp Type
V. Mag
a Vir
6 45.1
10 8.4
12 26.6
13 25.1
-16
11
-63
-11
43
58
7
10
-1.46
1.35
1.35
0.97
A1 V
B7 V
B0.5 IV + B1 V
B1 IV + B2 V
b Cen
a Lyr
s Sgr
a Pav
a Gru
a PsA
a Gru
a PsA
14 3.8
18 36.9
18 55.3
20 25.6
22 8.2
22 57.7
22 8.2
22 57.7
-60 22
38 47
-26 18
-56 44
-46 58
-29 37
-46 58
-29 37
0.61
0.03
2.02
1.94
1.74
1.16
1.74
1.16
B1 III
A0 Va
B2.5 V
B2.5 V
B7 IV
A3 V
B7 IV
A3 V
a Leo
a Cru
5. RADIANCE/REFLECTANCE DETERMINATION AND ERROR ANALYSIS
CIPS measures the radiance arriving at the input aperture of the instrument. This section
describes the conversion of instrument output (CCD detector data numbers, and ancillary
engineering values) to geophysical data (radiance) and the errors associated with those
conversions.
5.1
RADIANCE CONVERSION
The relationship between instrument output anc cloud albedo is given by:
Cloud Imaging and Particle Size Experiment
DN (i, j)Cloud  t   [ROpt (i, j,  )  QE Det (i, j,  ,T )  G Int (i, j,  ,HV )  Albedo(i, j,  )  FSun ( )]d

DN (i, j)Cloud = t   [RInst (i, j,  ,T ,HV )  Albedo(i, j,  )  FSun ( )]d

or,
where,
RInst  ROpt (i, j,  )  QE Det (i, j,  ,T )  G Int (i, j,  ,HV )
DN (i, j)Cloud  DN (i, j)Obs  DN Off  N CCD  DN (i, j) Background DN (i, j) Dark  DN (i, j) Stray
DN(i,j) is the data number from pixel i,j, acquired during integration time t, corrected for CCD
nonlinearity, NCCD, DNBackground, DNDark, and DNStray are corrections for background, dark, and

stray light. RInst is the instrument responsivity, which is the product of the optical response
(ROpt=transmission multiplied by etendue), intensifier quantum efficiency, (QEDet), and
intensifier gain (GInt). (QE*G has units of DN per photon arriving at the detector). And FSun is
the solar irradiance at the top of the atmosphere. The wavelength averaged albedo of the scene,
imaged onto pixel i,j is then given by:
Albedo(i, j)  DN (i, j)Cloud t   [RInst (i, j,  ,T ,HV ) FSun ( )]d

5.2 ERROR ANALYSIS

Error analysis
for the radiance calculation yields the uncertainty equation. Uncertainties are
expressed in percent, with the parameter naming (the subscript for each ) taken from equation
5.1.1 and with the pixel indices, temperature, and wavelength dependences suppressed.
2
2
 Albedo
  DN
  t2 
2
 DN

 R()  F()d
2
2
2
2
2
2
2
2
2
DN Obs
 N 2  ( Obs
  N2 )  DN Off
 N 2  ( Off
  N2 )  DN Bkg
  Bkg
 DN Dk
  Dk
 DN St2   St2
DN  DN  N  DN
Off

Bkg
 DN Dk  DN St

2
Equation 5.1.2 contains an implicit term for errors in the calibration measurements caused by
uncertainty in the position of the individual wavelength bands that are calibrated. Table 6 lists the
expected values for the uncertainties in equation 5.1.2. Responsivity is the most uncertain
parameter and leads to errors in the derived radiance that are directly proportional to its
magnitude. This does not impact the relative uncertainty in comparing two observations and
those measurements are limited by photon signal-to-noise.
6. REFERENCES
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Cloud Imaging and Particle Size Experiment
Table 6. Estimated Error Parameter Uncertainty
Parameter
Detector Signal (C)
Detector Dark (D)
Noninearity Correction. (N)
Light scattered into the pixel (SL)
Integration Time (t)
Resp. (R)
0.5%
0.5%
10%
10%
0.002%
FOV Map (
10-12%
10%
Wavelength ()
0.5%
Radiance
10-15%
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