The Ozone Mapping and Profiler Suite (OMPS) aboard the Joint Polar Satellite System-1 (JPSS-1) spacecraft is the 2nd Ultraviolet (UV) Sensor Suite launched on November 18, 2017. Similar to the OMPS on S-NPP, the OMPS on JPSS-1 (which is also named NOAA-20, or N20) contains two advanced nadir viewing hyper-spectral instruments, Nadir Profiler (NP) and Nadir Mapper (NM), to measure the total column and vertical profile of ozone in the atmosphere globally. This paper first briefly summarizes the status of calibration to OMPS on N20 sensor data record (SDR) at NOAA, which reached provisional maturity status on April, 2019 but more update on the stray light correction is on-going. An initial assessment of NOAA N20 SDR products are present in this paper. In these validations, we first compared the NP and NM spectral from N20 with the collocated spectral from S-NPP and TROPOMI. In addition, the radiative transfer model, TOMRAD, was used to simulate the radiance to be measured by OMPS NP and NM, and the inputs include the collocated ozone profiles from S-NPP and the total ozone amounts from either S-NPP or TROPOMI. Both simulations and spectral comparison with S-SNPP show that most channels meet the requirements with an accuracy of 2%, except in channels where the impact by stray light is large. However, the normalized reflectance of N20 is, on average, 10-30% smaller than TROPOMI. Due to the large spatial and spectral solution between OMPS and TROPOMI, further comparison by selecting the clear cases is needed. Results of this study provide useful information on NOAA-20 OMPS post-launch calibration assessment and preliminary analysis of its calibration stability and consistency with S-NPP. These two approaches through (1) the crosscomparison of spectral, and (2) the comparison with simulations, will be used to monitor the status of OMPS and improve the N20 OMPS radiance calibration at NOAA.
The Ozone Mapping and Profiler Suite (OMPS) on the National Oceanic and Atmospheric Administration Suomi National Polar-Orbiting Partnership spacecraft has completed three more years of orbital operation since the OMPS opened its nadir door for the scene data collection on January 26, 2012. The sensors’ spectral channels have been calibrated in-flight by a working solar diffuser and a reference solar diffuser. The instruments’ optical degradation is determined through the changes in the instruments’ throughput via orbital solar observations. The observed degradation at the shortest wavelengths is <1% for the sensor optics, and in excess of 2% for the OMPS working solar diffuser. The absolute irradiance calibration uncertainties meet the system requirement of 7% for most of the channels. Unexpected orbital wavelength variation in sensor scan direction is evidenced to cause about 2.6% error, not compliant with a 2% allocation and so some margin will be needed to accommodate the exceedance.
This paper analyzes the in-flight performance of the Suomi National Polar-orbiting Partnership Ozone Mapping & Profiling Suite (OMPS) nadir instruments and evaluates sensors’ on-orbit calibrations after sensors’ two-year operation. All uncertainty values quoted in this paper are 1−σ values unless stated otherwise. With the data collected from in-flight nominal calibration, our results have demonstrated that sensor performance complies with the system specifications in most cases. The largest term in the wavelength-dependent albedo calibration uncertainty for Nadir Mapper is the cross-track position difference effect of 2.5%. Final adjustments of stray light and wavelength variation are still being made to optimize OMPS sensor data records before reaching the validation mature level.
OMPS is the latest advanced hyperspectral sensor suite flying onboard the Suomi National Polar-Orbiting Partnership
(Suomi NPP) spacecraft. It measures ozone depletion in total column and vertical profile ozone abundances. OMPS on-orbit
calibration is conducted through dark, lamp and solar measurements. Launched on October 28, 2011, OMPS Nadir
has successfully undergone a thorough early orbit check (EOC) and is currently in the intensive calibration and
validation (ICV) phase. The calibration data gathered during the on-orbit calibration and validation activities allows us to
evaluate the sensor’s early orbit performance and establish on-orbit calibration baseline. In this paper, we provide details
of the sensor major on-orbit calibrations activities and present sensor level performance and calibration results from
OMPS early orbit image data. These results have demonstrated that the OMPS has made a smooth transition from
ground to orbit, and its early on-orbit performance meets or exceeds sensor level requirements and agrees with the
predicted values determined during the prelaunch calibration and characterization. Examples of Nadir CCD orbital
performance monitoring are provided.
The Ozone Mapping Profiler Suite (OMPS) was launched aboard the Suomi National Polar-orbiting Partnership (Suomi
NPP) spacecraft on October 28, 2011. OMPS is meant to continue NOAA/NASA's long-term ozone data record and
bridge the gap to the Joint Polar Satellite System (JPSS) missions later this decade. We present results from the OMPS
Nadir and Limb sensors' early orbit checkout (EOC) operations with comparisons to pre-launch thermal vacuum tests.
Characterization measurements of detector performance show that offset, gain, and read noise trends remain within 0.2%
of the pre-launch values with significant margin below sensor requirements. Nadir Total Column detector dark
generation rate trends show a slow growth in both halves of the focal plane as compared to initial on-orbit
Nadir solar calibration measurements remain within 2% of the initial in-flight observation and indicate no spatially
dependent change to within 1%. Limb Profiler solar calibration trending indicate a potential goniometry correction error
as high as 5%. Spectral registration changes based on solar observations are determined to be less than one pixel for the
Nadir Total Column and Limb sensors but approximately one pixel for Nadir Profiler. Preliminary comparisons to
Thullier reference solar spectral irradiances show wavelength dependent differences greater than 5%.
The MODIS (Moderate Resolution Imaging Spectroradiometer) scanner makes subframe measurements in some
of its bands to increase the spatial resolution from its standard 1km resolution to 500m or 250m. This is achieved
by sampling a detector of a high resolution band at twice (or four times) the sampling rate of the 1km bands.
This paper shows that a calibration equation nonlinear with radiance and specific to the individual subframes will
reduce striping in the images. The effects are significant for low radiance levels like those encountered over ocean
scenes. A preliminary calibration correction is derived with two approaches: first from prelaunch measurements,
then from on-orbit data. The results of the two methods are qualitatively similar.
The MODIS scan mirror reflectance is a function of angle of incidence (AOI). For the MODIS solar reflective bands
(RSB), it is specified that the calibrated response variation versus scan angle (RVS) should be less than 2% and the
uncertainty of the RVS characterization should be less than 0.5% within the scan angle range of -45° ~ +45°. During
MODIS pre-launch RVS calibration and characterization, a series of laboratory tests were performed to assess the
relative response versus scans angle for all MODIS bands. Utilizing a Spherical Integrating Source, SIS, as an
illumination source, the test data was collected at various angles of incidence. The characterization of the RVS included
a measurement uncertainty assessment, repeatability analysis, RVS modeling and determination. The results show good
repeatability on the order of less than 0.5% for all the near infrared (NIR) bands and the visible (VIS) bands. The
detector response variation across scan angles for the majority of the NIR and VIS bands meets the instrument
specification. The derived RVS model enabled appropriate implementation of on orbit calibration. This paper
summarizes the methodologies and the algorithms used in the MODIS pre-launch RVS calibration for the RSB bands,
illustrates detector response variation with scan mirror angle of incidence, and demonstrates instrument specification
compliance within the scan angle coverage of ±55 degree. As a result, the RVS model and the correction coefficients
developed in the pre-launch calibration have been adopted during the MODIS on-orbit calibration.
MODIS is a major instrument for NASA's EOS missions, currently operating aboard the EOS Terra and Aqua spacecraft
launched in December 1999 and May 2002, respectively. It was designed to extend heritage sensor measurements and
data records and to enable new research studies of the Earth's land, oceans, and atmosphere. MODIS has 36 spectral
bands (0.41 - 14.4μm) located on four focal plane assemblies (FPA). It makes measurements at three nadir spatial
resolutions: 0.25km, 0.5km, and 1km. Because of instrument design complexity and more stringent calibration
requirements, extensive calibration and characterization activities were conducted pre-launch by the sensor vendor for
both Terra and Aqua MODIS. For the 20 reflective solar bands (RSB) with wavelengths below 2.2μm, these activities
include detector noise characterization, radiometric response at different instrument temperatures and at different scan
angles, and relative spectral response. On-orbit RSB calibration is performed using a solar diffuser (SD) and a solar
diffuser stability monitor (SDSM). In addition, regular lunar observations are made to track RSB radiometric stability.
This paper provides a summary of Terra and Aqua MODIS RSB pre-launch and on-orbit calibration and characterization
activities, methodologies, data analysis results, and lessons learned. It focuses on major issues that could impact MODIS
RSB calibration and data product quality. Results presented in this paper include RSB detector noise characterization,
response versus scan angle and instrument temperature, SD bi-directional reflectance factors characterization, and on orbit
calibration stability. Similar discussions on MODIS thermal emissive bands (TEB) are presented in a separate paper in these proceedings (Xiong et. al).
The MODerate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands with wavelength ranging from 0.41(mu) to 14.5(mu) and spatial resolution of 0.25 km (2 bands), 0.5 km (5 bands), and 1.0 km (29 bands) at Nadir. Its ProtoFlight Model (PFM) on the NASA EOS Terra spacecraft has been providing global coverage of the Land, Ocean, and Atmosphere for the science community since the instrument opened its Nadir door on 24 February 2000. The MODIS optical system includes a 2-sided paddle wheel scan mirror, a fold mirror, and a primary mirror. The sensor's 20 reflective solar bands (RSB) from 0.41(mu) to 2.1(mu) are calibrated on- orbit by a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). In addition to the SD, degradation of the MODIS optics in the reflective solar bands has been observed, including variations in degradation between the two sides of the MODIS scan mirror. During MODIS first year of on-orbit operation, the overall degradation at the shortest wavelength of 0.41(mu) is about 2.5% for the SD, and in excess of 8% for the MODIS system. In this paper, we present our degradation analysis results and discuss their impact on the RSB on-orbit calibration.