Noaa Report on Suomi National Polar Orbiting Partnership (Npp) Calibration and Validtaion Results

CGMS-40, NOAA-WP-17 v1 12 October 2012 Prepared by F. Weng, Y. Han, Changyong Cao, and Chunhui Pan Agenda Item: II/2 Discussed in WG-II

NOAA REPORT ON SUOMI NATIONAL POLAR ORBITING PARTNERSHIP (NPP) CALIBRATION AND VALIDTAION RESULTS

Summary of the Working Paper

NOAA REPORT ON SUOMI NATIONAL POLAR ORBITING PARTNERSHIP (NPP) CALIBRATION AND VALIDTAION RESULTS

1 INTRODUCTION

The Suomi NPP (SNPP) satellite was launched successfully on October 28, 2011 and is a pathfinder for the future US Joint Polar Satellite System (JPSS) operational satellite series. The primary objectives of the SNPP mission provide a continuation of the group of Earth system observations initiated by the Earth Observing System Terra, Aqua, and Aura missions; and prepare the operational forecasting community with pre-operational risk reduction, demonstration, and validation for selected JPSS instruments and ground processing data systems. The SNPP satellite is now flying with the following five instruments: 1) Visible/Infrared Imager/Radiometer Suite (VIIRS) has multi-band imaging capabilities to support the acquisition of high-resolution atmospheric imagery and generation of a variety of applied products including visible and infrared imaging of hurricanes and detection of fires, smoke, and atmospheric aerosols. 2) Cross-track Infrared Sounder (CrIS) is the the first in a series of advanced operational sounders that provide more accurate, detailed atmospheric temperature and moisture observations for weather and climate applications. 3) Advanced Technology Microwave Sounder (ATMS) operates in conjunction with the CrIS to profile atmospheric temperature and moisture. Higher (spatial, temporal and spectral) resolution and more accurate sounding data from CrIS and ATMS support continuing advances in data assimilation systems and NWP models to improve short- to medium-range weather forecasts. 4) Ozone Mapping and Profiler Suite (OMPS) measures the concentration of ozone in the atmosphere, providing information on how ozone concentration varies with altitude. Data from OMPS continue three decades of climate measurements of this important parameter used in global climate models. The OMPS measurements also fulfil the U.S. treaty obligation to monitor global ozone concentrations with no gaps in coverage. 5) Cloud and Earth Radiant Energy System (CERES) seeks to develop and improve weather forecast and climate models prediction, to provide measurements of the space and time distribution of the Earth's Radiation Budget components. The observations from CERES are essential to understanding the effect of clouds on the energy balance (energy coming in from the sun and radiating out from the earth), which is one of the largest sources of uncertainty in our modelling of the climate. The SNPP instruments are now undergoing a period of intensive calval and the instrument on-orbit performances are stable and the post-launch results all meet or exceed the specifications. The SNPP SDR products have reached the provisional level at which users can order the data from NOAA archival and perform in-depth scientific research. NOAA is in charge of calibration of four SNPP instruments: ATMS, CRIS and VIIRS and OMPS. The critical SNPP calval tasks have been completed and the most recent calval results will be reported in following sections. . 2. Advanced Technology Microwave Sounder (ATMS)

2.1 ATMS Instrument Characteristics

ATMS is a total power radiometer and scans in a cross-track manner within ±52.77° with respect to the nadir direction. It has a total of 22 channels with the first 16 channels primarily for temperature soundings from the surface to about 1 kPa (~ 45 km) and the remaining channels for humidity soundings in the troposphere from the surface to about 200 kPa (~15 km). There are two receiving antennas: one serving channels 1-15 below 60 GHz, and the Page 2 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 other for channels above 60 GHz. Table 1 provides a comparison of channel characteristics between ATMS onboard Suomi NPP and AMSU-A/MHS (to be referred AMSU hereafter for simplicity) onboard NOAA-18, -19 and MetOp-A. ATMS has 22 channels while AMSU has 20 channels. Seventeen of ATMS channels (ATMS channels 1-3, 5-15, 17, 20 and 22) have the same frequencies as its predecessor AMSU (AMSU channels 1-14, 16-19), two ATMS channels (ATMS channels 16 and 18) have slightly different frequencies from AMSU channels (AMSU channels 15 and 20), and three new ATMS channels (ATMS channels 4, 19 and 21) are added. The ATMS channel 4 is new with its central frequency located at 51.76 GHz and contains temperature information in the lower troposphere that is much needed for NWP. The ATMS channels 19 and 21 are also new with their central frequencies located near 183-GHz water vapor absorption line (e.g., channel 19 at 183.31±4.5 GHz and channel 21 at 183.31±1.8 GHz) and are added for better profiling atmospheric moisture. There are two receiving antennas on ATMS: One serving 15 channels below 60 GHz and the other for seven channels above 60 GHz. Both antennas consist of a plane reflector mounted on a scan axis at a 45° tilt angle. The scan axis is oriented in parallel with the along- track direction, Radiation is reflected from a direction perpendicular to the scan axis into a direction along the scan axis (i.e., a 90° reflection), resulting in a cross-track scan pattern. This reflected radiation is then focused by a stationary parabolic reflector onto a dichroic plate where the energy is either reflected to or passed through to a feedhorn

2.2 ATMS On-Orbit Performance

The ATMS calibration algorithms involve determining the blackbody brightness temperature and a temperature dependent bias correction. Brightness temperatures of blackbody are measured by the embedded Platinum Resistance Thermometer (PRT). The blackbody and cold-space radiation components are sampled four times in each calibration cycle, and then averaged. These averaged values are further smoothed over several calibration cycles. The radiometer gain is calculated from the smoothed blackbody and cold-space radiation counts and is then used to estimate the Earth scene brightness temperature from a two-point linear calibration equation. The non-linearity amplitude is estimated using the difference between the measured instrument temperature and that from two-point calibration. This implicit transfer function is applied to the earth-scene counts for every scan cycle. The ATMS instrument noise is fully characterized during the period of the prelaunch and on-orbit calibration and is shown in Figure 1. In general, the ATMS noise equivalent differential temperature (NEDT) for temperature sounding channels is higher than the AMSU-A values mainly because the ATMS sampling time (e.g. the effective integration time for each FOV) is much shorter than that of AMSU-A. Specifically, The integration time (e.g., the FOV stepping time) for all ATMS channels is 18 ms, while that for AMSU-A channels 1- 2 and 3-15 is 165 ms and 158 ms, respectively. However, NEDTs derived from the prelaunch and on-orbit calibration are much smaller than the specification, and in particular the postlaunch ATMS instrument noise is close to the AMSU-A values for its temperature sounding channels except for upper stratospheric channels. For user communities who continue their AMSU-A-like applications with ATMS, the ATMS data remapped into the same resolution as the AMSU-A are also available from CLASS. The Backus-Gilbert method was used for the conversion from ATMS FOVs to AMSU-A FOVs. This method provides not only an optimal combination of measurements for determining the average brightness temperature within a specified region, but also a quantitative measure of the tradeoff between resolution and noise.

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Figure 1. ATMS Noise Equivalent Differential Temperature (NEDT) in comparison with AMSU-A/MHS. The ATMS channel number is indicated on the x-axis and the AMSU channel number is indicated in the figure in blue (Weng et al., 2012)

3. Cross-track Infrared Sounder (CrIS)

3.1 CrIS Instrument Characteristics

In its normal operation mode, Suomi NPP CrIS takes measurements of double-sided interferograms with maximum optical path difference (OPD) 0.8, 0.4, 0.2 cm for the long- wave (LW), mid-wave (MW) and short-wave (SW) bands, respectively. CrIS can also be operated to measure the interferogram with a maximum ODP of 0.8 cm for all the three bands. For each spectral band, there are nine detectors arranged into a 3x3 array on a focal plane. The detector size and its position on the focal plane are the key Instrument Line Shape (ILS) parameters. The interferogram is sampled with a digital convertor triggered by the fringes from a laser metrology system. Since the sampling laser wavelength must be precisely known, fringes from a Neon lamp are used to calibrate the laser wavelength, roughly once per orbit. The Neon wavelength is also a key ILS parameter. The CrIS scan swath width is 2200 km. During a typical 8-second measurement scan, CrIS collects 34 fields of regard (FORs), each of which contains 9 fields of view (FOVs). An instantaneous FOV maps to a nadir footprint of 14 km on the ground from an altitude of 824 km. In the 34 FOR scan data set, 30 are Earth scene (ES) views, 2 warm internal target (ICT) views and 2 deep space (DS) views. The ICT and DS provide two known temperature reference points for radiometric calibration. For each of the FOVs, SDR data set contains separately the LW, MW and SW interferograms. The CrIS SDR includes Earth scene radiance spectra for each of the three spectral bands in complex numbers. Only the real part of the spectrum contains valid radiance data. For a well calibrated spectrum, the values of imaginary part of the spectrum are near zero. The spectra are not apodized, as different users may require different apodiztion functions to smooth data. The two additional data points at each end of the spectra are reserved for users to perform spectral apodizaton. The CrIS Science raw data records (RDRs) received on ground consist of ES, ICT and DS interferograms and calibration data. All the CrIS calibration coefficient data are contained in the so-called Engineering packet (EP) created in 4-minute interval. It is part of the Science RDR data transmitted from the instrument to the ground. The Science telemetry packet obtained once every 8 second is also part of the Science RDR, which contains dynamic data ICT temperature measurements, supporting science calibration and geolocation calculation. Page 4 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 The RDRs are transformed by the SDR software into calibrated spectra in each of the three bands. The algorithm includes modules to load and sort data (pre-process) and convert interferograms to raw (un-calibrated) spectra by Fast Fourier Transform (FFT). The raw spectra are defined on the sensor frequency grid, which is determined by the laser metrology. The Fringe Count Error (FCE) handling module detects and corrects the phase error caused by the loss of one or more fringe of the laser metroloy, based on the analysis of the residual phase of spectra. The nonlinearity correction module corrects the nonlinearity effect for those detectors exhibiting significant nonlinearity by scaling the raw spectra with (1- 2a2V), where V represents the DC voltage at the detector/preamp and a2 is the so-called nonlinearity coefficient determined through the CalVal process. The radiometric calibration module performs a two-target calibration using the ICT and DS observations. Since the ICT is not a perfect black body, the module includes an ICT radiometric model that takes into account the emissivity, transmissions and temperatures of the various elements seen by the ICT. The post calibration filter is applied to damp the signal in the guard band. The spectral re-sampling module interpolates the spectra on user grid. The self-apodization removal (ILS correction) module corrects the spectral distortion caused by off-axis self apodiztion. The residual ILS removal module removes the effect due to non-uniform modulation efficiency versus OPD. The Geolocation module computes the geolocation for each FOV.

3.2 CrIS on-Orbit Performance

The CrIS correlated and uncorrelated noise is characterized by computing Noise Equivalent Differential Radiance (NEdN) of the spectral data from ICT, DS and ES and estimating contributions of random and spectrally correlated components using the Principle Component Analysis (PCA) method. Figure 2 shows typical NEdN spectra computed from 30 ICT consecutive spectra. It can be seen that the NEdN spectra are well below the specification, except that for MW FOV7, which was an issue known before NPP launch.

Figure 2. CrIS Noise Equivalent Differential Radiance (NEdN) as a function of wavenumber.

The objective of the spectral calibration is to compute the frequency scale with an accuracy of 10ppm or better for all three bands. To do so, the Neon lamp wavelength and ILS parameters for each of the FOVs must be accurately determined, as they can be changed by launch vibrations and thermal variations. Two methods have been applied to evaluate and derive these parameters. One is to adjust detector positions on the focal plane until radiance spectra from all 9 detectors have the same frequencies in the observed radiance spectra for each of the spectral bands. The other method is to adjust Neon bulb wavelength until observed radiance spectra agree with the predicted spectra computed using a radiative transfer model (RTM) with the atmospheric states provided by a numerical weather prediction model (NWP). The outcome of the spectral calibration work is a new set of FOV positions Page 5 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 parameters, which were included in Engineering Packet version 33 and the conclusion that the Neon frequency has been very stable and has not changed significantly so far from its prelaunch value. Validation results show that the spectral frequencies for each FOV and spectral band have achieved an accuracy of 2 ppm. During the pre-launch ground tests and evaluations, a number of LW and MW detectors showed significant nonlinearity. The nonlinearity correction coefficient a2 for each of MW and LW detectors was first determined with the pre-launch experimental data. They were then refined and verified using in-orbit data in three processes. First, the diagnostic mode data collected during EOC were analyzed. The diagnostic mode data were interferograms after analog to digital conversion but before the digital filtering and data decimation for data rate reduction. The diagnostic data retain a portion of the spectrum, namely out-of-band spectrum, on each side of the desired in-band spectrum. For a detector with measurable nonlinearity, there will be significant signal in both the out-of-band regions. Since the out-of-band signal with higher frequencies are mixed with other signals not due to linearity distortion, the out-of- band signal with lower frequencies is used to estimate the a2 coefficients. The second process is to further adjust the a2 coefficients by comparing Earth scene observations among different FOVs, especially to the detectors with good linearity. The third process is to verify and assess the results by comparing CrIS measurements with those from the hyper-spectral Infrared Atmospheric Sounding Interferometer (IASI) and Atmospheric Infrared Sounder (AIRS). The adjustment of the a2 coefficients results in significant improvement of the radiometric accuracy and performance uniformity among the 9 FOVs for the LW and SW bands. Figure 3 shows the differences between the observed and RTM simulated spectra after the biases are removed, which are the differences between the two, averaged over all FOVs. The black curves and blue curves are from the data before and after the a2 coefficient and the ILS parameter updates. It can be seen that the non-uniformity of the radiometric uncertainties among different FOVs have been reduced significantly, well below the 0.1 K level.

Figure 3. The differences between the observed and CRTM simulated spectra. The black curves are from the data before the a2 coefficient and ILS parameter updates. The blue curves are from the data after the a2 adjustments but before ILS parameter updates. The red curves are from data after both a2 and ILS parameter adjustments.

The spectral and radiometric uncertainty after the a2 coefficient and ILS parameter adjustments is evaluated by comparing collocated CrIS spectra with IASI and AIRS spectra. The result was preliminary, as the size of the data samples was limited. Figure 4 shows an example of the comparison between CrIS and IASI (re-sampled to CrIS resolution) spectra near in the North Pole region, using the Simultaneous Nadir Observation technique (SNO). It can be seen that the overall difference of the radiances after the both a2 and ILS parameter adjustment is about 0.1 K. Page 6 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012

Figure 4. Comparison between CrIS and IASI (re-sampled to CrIS resolution) spectra in the North Pole region, using the SNO technique. Sample size = 344.

4. Visible/Infrared Imager/Radiometer Suite (VIIRS)

4.1 VIIRS Instrument Characteristics

VIIRS instrument builds on the success of several heritage sensors including AVHRR, MODIS, SeaWiFS, and OLS with 22 spectral bands: 5 I(image) bands, 16 M (moderate resolution) bands, and 1 DNB (day and night) bands, covering wavelengths from 0.41 to 12.5 µm. Several key design features make it a superior sensor compared to the predecessors. First, the VIIRS swath width is 3000 km across track which ensures the full coverage of the Earth between orbits without gap, compared to the 2330 km swath width of MODIS. This enables a complete global coverage in a day with 14 orbits. Second, the rotating telescope significantly improves the geometric quality of the pixels better preserving the pixel shape across the entire scan, especially compared to AVHRR where significant pixel rotation occurs towards the end of the scan. Third, the problem of pixel growth in traditional sensors is controlled by an over-sampling and zonal aggregation scheme. This makes the pixel size at the end of the scan more comparable to that at the nadir, and therefore makes the image quality more uniform across scan, allowing the creation of nearly seamless global images from multiple orbits. Spectrally, the VIIRS has 22 bands covering the 0.4-12.5 um, compared to the 36 MODIS bands with a broader spectral range. The spectral bands absent in VIIRS are mostly atmospheric bands covered by the MODIS. A majority of the VIIRS bands have broader band width compared to that of the MODIS equivalent bands, although they are significantly narrower than the corresponding AVHRR bands. The Day Night Band (DNB) represents a new capability that is not available in the predecessors MODIS and AVHRR. The DNB significantly outperforms the OLS on DMSP satellites because of its finer resolution of 750m, compared to the 2.7 km resolution for OLS. It is also noted that unlike OLS which has no onboard calibration, the DNB fully utilizes the onboard calibration system which makes it effectively the night observing radiometer. The seven dual gain radiometric bands are designed to accommodate a large dynamic range in the observed radiances. The low gain is designed to observe high reflectance objects or phenomena such as clouds and desert without saturation, while the high gain is used to amplify the low signals such as ocean color. This is in contrast to MODIS which uses single gain for all bands, while similar to some of the later AVHRR bands which also use dual gain. It is known that while dual gain has its advantages, its calibration does present more challenges, especially near the gain transition region.

Page 7 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 4.2 VIIRS on-Orbit Performance

The Suomi NPP VIIRS was turned on 8th November, 2011 for measuring reflective band radiance. The VIIRS Cryo-cooler door was opened on 18th January 2012, starting the observations for thermal emissive bands. The VIIRS bands are calibrated radiometrically using the onboard calibration system, which has many similarities to that of the MODIS. For the reflective solar bands (RSB), the two-point calibration system consists of the solar diffuser and the space view. The solar diffuser calibration occurs once per orbit in the southern hemisphere as the satellite going southward out of the night portion of the orbit. Since there is no solar diffuser door in the VIIRS design, the solar diffuser is always exposed to sun light at this location which potentially accelerates the solar diffuser degradation. An attenuation screen is used to reduce the solar irradiance to a level that makes the high calibration point more comparable with that the earth view signal for most bands. The solar diffuser bidirectional reflectance distribution function (BRDF) was characterized prelaunch and is used in determining the calibration points and related calibration coefficients. Separately, the stability of the solar diffuser is monitored using the SDSM (Solar Diffuser Stability Monitor), which uses the ratio between solar and diffuser observations to determine the reflectance change in the solar diffuser. Assuming that the solar intensity is constant, any change in this ratio would indicate a change in the solar diffuser itself. It is also noted that the SDSM detectors can degrade over time, primarily due to impacts from high energy particles, but its effect are mostly cancelled out in the ratio. For the thermal emissive bands (TEB), or thermal infrared bands, the two calibration points consist of the onboard blackbody and the space view. The blackbody temperature is maintained at ~292 K at all times while the brightness temperature of the deep space is extremely low with practically zero radiance. There are six platinum resistance thermometers (PRTs) in the blackbody which accurately measure the temperature, and the blackbody radiances are computed using the Planck function in the calibration process. Although the photovoltaic detectors used in VIIRS have linear response to incoming radiation on the first order, a nonlinear equation is used for calibrating the radiance to account for any small nonlinearity observed in prelaunch thermal vacuum testing. In addition, Warm Up Cool Down (WUCD) of the blackbody is performed on VIIRS quarterly to monitor any changes in the system response including nonlinearity. VIIRS significantly outperforms the legacy of current operational sensor AVHRR in spatial, spectral, and radiometric areas by design. The 22 spectral bands in the visible, near- infrared, mid-infrared, and long-wave infrared regions of the electromagnetic spectrum are acquired at two spatial resolutions: 0.375 km for imagery bands, and 0.75 km for moderate resolution radiometry bands at nadir. Using a pixel aggregation strategy and manages data compression with several strategies including the so-called “bow-tie” removal, the VIIRS achieves a resolution of 0.8 km for imagery bands, and 1.6 km for moderate resolution radiometry bands at the edge of scan. VIIRS uses six dual-gain reflective bands to provide the high radiometric resolution needed for ocean color applications, at the same time without saturating the sensor when observing high reflectance surfaces such as land and clouds. The dynamic range of the dual gain bands in high gain is comparable to that of the MODIS ocean color bands, while the dynamic range in the low-gain state is comparable to those of the similar MODIS land bands. The dynamic ranges across all other bands are similar to their MODIS counterparts. VIIRS has one dual-gain thermal emissive band (M13) to measure fire temperature at a low gain and normal surface temperature at a high gain. The panchromatic DNB band measures night lights, reflected solar and/or moon lights with a large dynamic range of 45,000,000:1, which allows the detection of reflected signals from as low as quarter moon illumination to the brightest daylight. To achieve this large dynamic range it uses a three-stage focal plane. The sensor maintains a nearly constant 0.75 Page 8 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 km resolution over the entire 3000-km swath using an on-board aggregation scheme. After subtracting background noise, the VIIRS DNB shows a beautiful image of cities’ light and moon light reflected by clouds. Table 1. VIIRS performance met the specification. Signal to ratio is used for reflective spectral band and NEdT is used for thermal emissive band. The on-orbit performance and uncertainty are averaged from AeroSpace, NASA, and NOAA/STAR teams.

The VIIRS SDR team found and resolved many discrepancies in sensor and ground procession system. Scan-line based update of calibration tables has been developed and implemented to compensate the VIIRS RTA mirror degradation due to tungsten contaminations. Through spacecraft maneuvers, the team precisely determined the solar diffuser stability monitor (SDSM) screen transmittance and solar diffuser (SD) screen transmittance as well as the SD BRDF behaviours. It was found that 2 of 6 PRTs experienced a small periodic variation of 60 mK per orbit, correlated with solar zenith angles. Independent evaluations of the VIIRS sensor from Aerospace, NASA, and NOAA showed that the VIIRS SDR achieved excellent geolocation accuracy of better than 100 meters and the radiance performance met the specification. The VIIRS SDR team also developed methodologies to estimate band to band registration error with lunar calibration. The VIIRS image quality is excellent.

5. Ozone Mapping and Profiler Suite (OMPS)

5.1 OMPS Instrument Characteristics

OMPS is one of ozone monitoring sensors in a series of remote-sensing instruments flown by NOAA and NASA. It continues more than 30 years ozone study mission by providing the users with the atmospheric ozone products. OMPS sensor suite comprises three instruments, Nadir Mapper (NM), Nadir Profiler (NP) and Limb Profiler (LP). The Nadir system has two grating spectrometers that provide a spectral resolution of 0.4 nm in spacing Page 9 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012 and 1 nm in full-width half-maximum (FWHM), covers spectral wavelength from 250 to 310 nm for the NP with 146 spectral channels and 300 nm to 380 nm for the NM with 196 spectral channels. In the Earth’s observation, OMPS cross-track field of view (FOV) is co-bore sighted between the NP and the NM, where the NP has a 16.6° cross-track FOV providing ozone profiles in a single ground pixel of 250x250 km at nadir while the NM has a 110° scan swath and provides the ozone total column measurement in 38 ground pixels cross 3800 km earth view swath with a spatial resolution of 50x50 km at nadir. OMPS focal plan arrays (FPAs) consist of two-dimensional CCD optical detectors that are used for each spectrometer to provide sensor response within the spectral range. The CCD optical detectors have 364 spectral wavelengths. During OMPS NM earth observation, 780 pixels in each scan are spatially binned into 38 macropixels, including two binned smear pixels, to provide a 3.15 degree IFOV at nadir. The NP CCD has 364 spectral wavelengths and collects 390 spatial pixels that are spatially binned into one macropixel with cross-track IFOV matches to the central five NM macropixels. In collection of a CCD image data, pixels inside of the CCD image (photosensitivity) regions collect signal over a predetermined integration time period. These collected pixels are transferred to the CCD storage regions on each side of the photosensitive regions within a short transfer time period, and then processed horizontally line by line through CCD read out amplifiers. The CCD read out register extends beyond the CCD edges with 12 serial over-clock pixels in the spectral direction on the top (trailing) and bottom (leading) of the CCD and 20 smear pixels in the spatial direction on both sides of the CCD. These over-clocked pixels are used to estimate electronic offsets and they are read out together with every CCD row within the photosensitive regions.

5.2 OMPS on-Orbit Performance

OMPS on-orbit calibration is performed through the measurements of dark current, linearity, solar irradiance and earth view observation. Two onboard calibrators, Light- Emitting Diodes (LEDs) and Solar Reflective Diffusers are used to provide the linearity calibration and solar observation, respectively. OMPS radiometric calibration of the earth- view radiances is determined by a ratio of observed radiance to observed irradiance at the same wavelength to an accuracy greater than or equal to 2% at all wavelengths from 250-380 nm. During the nominal operation, earth view science data is collected during the portion of the NPP orbit sunlight side from solar zenith angle -88 to +80 degree, and solar calibration data collection is performed over the North Pole from solar zenith angle +80 to +100 degree, then followed by collection of linearity and dark current images on the dark side of the earth with the Nadir diffuser in the closed position. OMPS on-orbit characterizations of detector performance show that sensor electronic bias, detector gain, dark smear, dark current rate, and linearity remain are within 0.2% of the prelaunch values with significant margin below sensor requirements. Detector gain and bias performance trends are generally stable. System linearity performance exhibits excellent stability and highly consistent with the prelaunch values. Changes in dark current due to transients and hot pixels are within our expectations and the constant increase of the dark current suggest a daily update of the dark calibration table is necessary. Solar measurement (signal to noise ratio SNR) meets the system requirement of 1000. Day one solar irradiance and day one wavelengths have been established, which is within an average of 2% of predicted values. For NP, stray light is present and our preliminary analysis shows a correlation of the signal at 280-nm with that at 305-nm gives 3%: 50% response ratio. OMPS geolocation is generally good at 5 km level (Small FOV) with an intra-orbit wavelength scale stability of 0.02-nm. OMPS nonlinearity meets the system requirement of 2%.

6. Summary Page 10 of 11 CGMS-40, NOAA-WP-17 v1 12 October 2012

The Suomi NPP ATMS, CrIS, VIIRS and OMPS are performing very well in orbit, exceeding user expectations. The key parameters of all the instruments meet the specification with large margins. The new design features are advantageous compared to those for its predecessor sensors in many aspects which will enable unique capabilities for many potential new applications. The data maturity has reached beta status in early spring and provisional status is expected by fall 2012. The unexpected fast degradation in VIIRS bands centered at 0.86um is being mitigated through more frequent updates of the calibration lookup tables and the strategy is working well with minimal residual impacts.

7. References

Butler, J. X. Xiong, R. A. Barnes, F. S. patt, J. Sun, K. Chiang, An overview of NPP VIIRS calibration maneuvers, Proceedings of SPIE, Earth Observing Systems, 2012. Cao, C., X. Xiong, F., Deluccia, F. Weng, 2012, Early On-orbit Performance of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar- orbiting Partnership (SNPP) Satellite, submitted to IEEE TGRS Deluccia, F, and C. Cao, 2012, NPP VIIRS Instrument Characteristics, Measurements and Sensor Data Record Production, AMS 2012, New Orleans Weng, F., X. Zou, X. Wang, S. Yang, M. Goldberg, 2012: Introduction to Suomi NPP ATMS for NWP and Tropical Cyclone Applications, J. Geophys. Res., doi:10.1029/2012JD018144

ACKNOWLEDGEMENTS I would like to thank the entire Suomi NPP SDR team leads for providing all the technical materials for this report and their dedicated support to the NPP postlaunch cal/val. This work is funded by the JPSS program office. The manuscript contents are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of NOAA or the U.S. government.

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