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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) Page 2 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 Instrument Calibration Plan (ICP) Page 3 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 Instrument Calibration Plan (ICP) Page 4 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 Instrument Calibration Plan (ICP) Page 5 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. Instrument Calibration Plan (ICP) Page 6 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. Instrument Calibration Plan (ICP) Page 7 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 Instrument Calibration Plan (ICP) Page 8 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. Page 9 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) Page 10 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) Page 11 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 Page 12 CTEII 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 Instrument Calibration Plan (ICP) Page 13 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) Page 14 Table 5. Pre and Post Launch Calibration Activities Function Parameter Notes Stray and Scattered Light Telescope Off-axis Light Measure over ~ 2Check 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 Place holder 1 Instrument Calibration Plan (ICP) Page 2 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% Instrument Calibration Plan (ICP) Page 3