Glen Jaross

Ozone monitoring instrument calibration

The Ozone Monitoring Instrument (OMI) was launched on July 15, 2004 on the National Aeronautics and Space Administrations Earth Observing System Aura satellite. The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional charge-coupled device detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115/spl deg/ wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents the OMI design and discusses the main performance and calibration features and results.

Validation of Ozone Monitoring Instrument level 1b data products

[1] The validation of the collection 2 level 1b radiance and irradiance data measured with the Ozone Monitoring Instrument (OMI) on NASA’s Earth Observing System (EOS) Aura satellite is investigated and described. A number of improvements from collection 2 data to collection 3 data are identified and presented. It is shown that with these improvements in the calibration and in the data processing the accuracy of the geophysically calibrated level 1b radiance and irradiance is improved in the collection 3 data. It is shown that the OMI level 1b irradiance product can be reproduced from a high-resolution solar reference spectrum convolved with the OMI spectral slit functions within 3% for the Fraunhofer structure and within 0.5% for the offset. The agreement of the OMI level 1b irradiance data product with other available literature irradiance spectra is within 4%. The viewing angle dependence of the irradiance and the irradiance goniometry are discussed, and improvements in the collection 3 data are described. The in-orbit radiometric degradation since launch is shown to be smaller than 0.5% above 310 nm and increases to about 1.2% at 270 nm. It is shown how the viewing angle dependence of the radiance is improved in the collection 3 data. The calculation of the surface albedo from OMI measurement data is discussed, and first results are presented. The OMI surface albedo values are compared to literature values from the Total Ozone Mapping Spectrometer (TOMS) and the Global Ozone Monitoring Experiment (GOME). Finally, improvements in the spectral and spatial stray light corrections from collection 2 data to collection 3 data are presented and discussed.

Calibration and postlaunch performance of the Meteor 3/TOMS instrument

Prelaunch and postlaunch calibration results for the Meteor 3/TOMS instrument are presented here. The instrument, launched aboard a Russian spacecraft in 1991, is the second in a series of total ozone mapping spectrometer (TOMS) instruments designed to provide daily global mapping of ozone overburden. Ozone amounts are retrieved from measurements of Earth albedo in the 312- to 380-nm range. The accuracy of albedo measurements is primarily tied to knowledge of the reflective properties of diffusers used in the calibrations and to the instruments wavelength selection. These and other important prelaunch calibrations are presented. Their estimated accuracies are within the bounds necessary to determine column ozone to better than 1%. However, postlaunch validation results indicate some prelaunch calibration uncertainties may be larger than originally estimated. Instrument calibrations have been maintained postlaunch to within a corresponding 1% error in retrieved ozone. Onboard calibrations, including wavelength monitoring and a three-diffuser solar measurement system, are described and specific results are presented. Other issues, such as the effects of orbital precession on calibration and recent chopper wheel malfunctions, are also discussed.

Meteor 3/total ozone mapping spectrometer observations of the 1993 ozone hole

The development of the springtime (September–November) Antarctic ozone hole was observed by the Meteor 3/total ozone mapping spectrometer (TOMS) to result in the lowest ozone value, 85 DU (Dobson units) on October 8, 1993, ever measured by TOMS. During late September and early October the region of extremely low ozone values was centered on the geographical pole between 85°S and 90°S. The geographical extent of the ozone hole region, the area within the 220-DU contour, reached a maximum during the first week in October at a near-circular area covering 24×106 km2 reaching to the southern tip of South America. This approximately matched the 1992 area record. After the maximum area was reached in early October, the 1993 ozone hole region was significantly larger than during 1992 throughout the remainder of the month of October. The very low ozone values over the Antarctic continent have been confirmed by independent ground-based data. Unlike 1992, the formation of the 1993 Antarctic ozone hole does not coincide with unusually low ozone values observed over most of the globe for the past 2 years. The most recent ozone data from Meteor 3/TOMS show that there has been a recovery at all latitudes from the extraordinarily low values observed during 1992 and part of 1993 after the June 1991 eruption of Mount Pinatubo. Meteor 3/TOMS is described and compared with Nimbus 7/TOMS during the 1991 to May 1993 overlap period. Observations of the 1992 ozone hole are presented from both instruments and are shown to agree within 5 DU.

OMPS Limb Profiler Instrument Performance Assessment

Following the successful launch of the Ozone Mapping and Profiler Suite (OMPS) aboard the Suomi National Polar-orbiting Partnership (SNPP) spacecraft, the NASA OMPS Limb team began an evaluation of instrument and data product performance. The focus of this paper is the instrument performance in relation to the original design criteria. Performance that is closer to expectations increases the likelihood that limb scatter measurements by SNPP OMPS and successor instruments can form the basis for accurate long-term monitoring of ozone vertical profiles. The team finds that the Limb instrument operates mostly as designed and basic performance meets or exceeds the original design criteria. Internally scattered stray light and sensor pointing knowledge are two design challenges with the potential to seriously degrade performance. A thorough prelaunch characterization of stray light supports software corrections that are accurate to within 1% in radiances up to 60 km for the wavelengths used in deriving ozone. Residual stray light errors at 1000 nm, which is useful in retrievals of stratospheric aerosols, currently exceed 10%. Height registration errors in the range of 1 km to 2 km have been observed that cannot be fully explained by known error sources. An unexpected thermal sensitivity of the sensor also causes wavelengths and pointing to shift each orbit in the northern hemisphere. Spectral shifts of as much as 0.5 nm in the ultraviolet and 5 nm in the visible, and up to 0.3 km shifts in registered height, must be corrected in ground processing.

Postlaunch Performance of the Suomi National Polar-Orbiting Partnership Ozone Mapping and Profiler Suite (OMPS) Nadir Sensors

The prelaunch specifications for nadir sensors of the Ozone Mapping and Profiler Suite (OMPS) were designed to ensure that measurements from them could be used to retrieve total column ozone and nadir ozone profile information both for operational use and for use in long-term ozone data records. In this paper, we will show results from our extensive analysis of the performance of the nadir mapper (NM) and nadir profiler (NP) sensors during the first year and a half of OMPS nadir operations. In most cases, we determined that both sensors meet or exceed their prelaunch specifications. Normalized radiance (radiance divided by irradiance) measurements have been determined to be well within their 2% specification for both sensors. In the case of stray light, the NM sensor is within its 2% specification for all but the shortest wavelengths, while the NP sensor is within its 2% specification for all but the longest wavelengths. Artifacts that negatively impacted the sensor calibration due to diffuser features were reduced to less than 1% through changes made in the solar calibration sequence. Preliminary analysis of the disagreement between measurements made by the NM and NP sensors in the region where their wavelengths overlap indicates that it is due to shifts in the shared dichroic filter after launch and that it can be corrected. In general, our analysis indicates that both the NM and NP sensors are performing well, that they are stable, and that any deviations from nominal performance can be well characterized and corrected.

Evaluation of the Sensor Data Record from the nadir instruments of the Ozone Mapping Profiler Suite (OMPS)

This paper evaluates the first 15 months of the Ozone Mapping and Profiler Suite (OMPS) Sensor Data Record (SDR) acquired by the nadir sensors and processed by the National Oceanic and Atmospheric Administration Interface Data Processing Segment. The evaluation consists of an inter-comparison with a similar satellite instrument, an analysis using a radiative transfer model, and an assessment of product stability. This is in addition to the evaluation of sensor calibration and the Environment Data Record product that are also reported in this Special Issue. All these are parts of synergetic effort to provide comprehensive assessment at every level of the products to ensure its quality. It is found that the OMPS nadir SDR quality is satisfactory for the current Provisional maturity. Methods used in the evaluation are being further refined, developed, and expanded, in collaboration with international community through the Global Space-based Inter-Calibration System, to support the upcoming long-term monitoring.

The ozone mapping and profiler suite (OMPS): on-orbit calibration design

The Ozone Mapping and Profiler Suite (OMPS) will collect total column and vertical profile ozone data and continue the daily global data produced by the current operational satellite monitoring systems, the Solar Backscatter Ultraviolet radiometer (SBUV/2) and the Total Ozone Mapping Spectrometer (TOMS), but with higher fidelity. The collection of this data will contribute to fulfilling US treaty obligations to monitor ozone depletion for the Montreal Protocol. OMPS has been selected to fly on the National Polar-Orbiting Operational Satellite System (NPOESS) spacecraft - the next generation of polar orbiting environmental satellites. The first OMPS flight unit will fly on the NPOESS Preparatory Project (NPP) spacecraft. On-orbit calibration of the OMPS instruments is critical to maintaining quality data products. A number of signal corrections and calibrations are applied on-board the sensor and in ground processing to account for instrument non-idealities and to convert measured digital signals to calibrated radiances and irradiances. Three fundamental on-orbit calibration measurements are made to provide the required data to perform the radiometric calibration and trending.

TOMS/ADEOS instrument characterization

Data sets from the total ozone mapping spectrometer (TOMS) on the ADEOS I spacecraft have been processed using initial and time-dependent instrument characterizations. Initial characterizations, performed on the ground, focused on wavelength registration of the six near-UV TOMS channels and on the instrument albedo calibration. Few calibration adjustments were required in the postlaunch phase. Instrument performance, including bandpass wavelengths, were stable throughout the life of the instrument. Indirect evidence exists for small changes in the reflectance of the primary solar diffuser. Characterizations used in data processing assume no change. No ozone retrieval errors are expected due to this assumption. All totaled, estimated calibration uncertainties represent less than 1% in total column ozone uncertainty. A comparison between two TOMS instruments is marginally consistent with these estimates. However, a comparison with ground measurements resulted in differences exceeding 1%.

The Meteor 3/total ozone mapping spectrometer version 7 data set: Calibration and analysis

The Meteor 3/total ozone mapping spectrometer (TOMS) data set has been reprocessed using the version 7 TOMS total ozone algorithm and a recalibration of the TOMS instrument using in-flight and revised laboratory data. To provide continuity for the analysis of long-term trends, the absolute calibration of Meteor 3/TOMS was adjusted so that the measured radiances closely matched Nimbus 7/TOMS. The residual bias in ozone is less than 1% and shows no significant latitudinal or seasonal dependence. The calibration procedure and the differences between the current and previously used calibrations are discussed. Problems in the Meteor 3/TOMS data set caused by chopper wheel synchronization problems are described, and comparisons of the resulting data with version 7 of the Nimbus 7/TOMS data are presented.