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Performance of the ozone mapping and profiler suite (OMPS) products

L. Flynn, C. Long, X. Wu, R. Evans, C.T. Beck NOAA

I. Petropavlovskikh,G. McConville CIRES

W. Yu, Z. Zhang, J. Niu,E. Beach, Y. Hao IMSG

C. Pan, UMD CICS

B. Sen, M. Novicki Northrop Grumman Aerospace Systems

S. Zhou, Wyle Information Systems

C. Seftor, SSAI

Corresponding author: Lawrence E. Flynn, NOAA, NCWCP E/RA2, 5830 University Research Court, #2850, College Park, MD 20740-3818 ()

Key Points

• OMPS nadir total column ozone and ozone profile products are performing well

• Deficiencies have been identifiedbut the remedies are known

• Further improvements to the SDR will be implemented in the system soon

Index Terms

3360 Remote Sensing

0340 Middle atmosphere: composition and chemistry

3311 Clouds and aerosols

“Manuscript Submitted for the Special Issue of AGU JGR-Atmospheres on Suomi NPP Cal/Val Science Results”.

Abstract. NOAA, through the Joint Polar Satellite System (JPSS) program, in partnership with National Aeronautical and Space Administration (NASA), launched the Suomi National Polar-orbiting Partnership (S-NPP) satellite, a risk reduction and data continuity mission, on October 28, 2011. The JPSS program is executing the S-NPP Calibration and Validation (Cal/Val) program to ensure the data products comply with the requirements of the sponsoring agencies. The Ozone Mapping and Profiler Suite (OMPS)consists of two telescopes feeding three detectors measuring solar radiance scattered by the Earth's atmosphere directly and solar irradiance by using diffusers. The measurements are used to generate estimates of total column ozone and vertical ozone profiles for use in near-real time applications and extension of ozone climate data records. The calibration and validation efforts are progressing well, and both Level 1 (Sensor Data Records/SDRs) and Level 2 (Ozone Environmental Data Records/EDRs) have advanced to release at Provisional Maturity. This paper provides information onthe product performance over the first 22 months of the mission. The products are evaluated through the use of internal consistency analysis techniques and comparisons to other satellite instrument and ground-based products. The initial performance finds total ozone showing negative bias of 2 to 4% with respect to correlative products and ozone profiles often within ±5% inthe middle and upper stratosphere of current operational products. Potential improvements in the measurements and algorithms are identified. Thesewill be implemented in coming months to reduce the differences further.

1. Introduction

The OMPS is composed of three instruments, called the Nadir Mapper (OMPS-NM), Nadir Profiler (OMPS-NP), and Limb Profiler (OMPS-LP).The OMPS-NM is a total ozone column sensor and uses a single grating and a Charge-Coupled Device (CCD) array detector to make measurements every 0.42 nm from 300 nm to 380 nm with 1.0-nm Full-Width Half-Maximum (FWHM) resolution. It has a 110° cross-track FOV (~2800 km on the Earth’s surface) and 0.27° along-track slit width FOV. In standard Earth science mode, the measurements are combined into 35 cross-track bins [20 spatial pixels giving 3.35° (50 km) at nadir, and 2.84° at ±55° cross-track dimensions for the FOVs]. The resolution is 50 km along-track at nadir, created by using a 7.6-second reporting/integration period. This resolution choice is changeable; andthe use of smaller FOVsand shorter integration times is under investigation.

The OMPS-NP is an ozone profile sensor and uses a double monochromator and a CCD array detector to make measurements every 0.42 nm from 250 nm to 310 nm with 1.1-nm resolution. It has a 16.6° cross-track FOV, 0.26° along-track slit width. The measurements are combined (100 spatial pixels) into a single spectrum and the reporting period is 38 seconds giving it a 250 km × 250 km cell size collocated with the five central OMPS-NMFOVs.

The OMPS-LP is a high vertical resolution ozone profile sensor and uses a prism spectrometer with spectral coverage from 290 nm to 1000 nm. It has three slits separated by 4.25° (viewing back along the nadir track and 250 km cross-track on either side at the tangent point) with a 19-second reporting period that equates to 125 km along-track motion. The slits have 112 km (1.95°) vertical FOVs equating to 0 to 60 km coverage at the limb, plus offsets for pointing uncertainty, orbital variation, and Earth oblateness. The CCD array detector provides measurements every 1.1 km with 2.1-km vertical resolution. There are two apertures into the instrument creating a total of six images on the CCD. Further the CCD array is read out with long and short integration times to produce four effective gains.

The OMPS instruments and measurements are described further in Rodriguez et al. [2003] and Remund et al. [2004] and inthree companion papers within this special issue:Seftor et al. [2013], Jaross et al. [2013] and Wu et al. [2013]. Of note is their use of working and reference solar diffusers to monitor instrument throughput degradation and maintain good calibration of the radiance/irradiance ratios used in the retrieval algorithms. Key updates to the SDRs are discussed in the companion papers. Of special interest for the OMPS-NM products are the implementation of a stray light correction, identification of intra-orbit wavelength scale variations, and estimation of calibration offset for OMPS through vicarious and internal consistency checks. For the OMPS-NP the key items are the same as for the OMPS-NMwith an additional refinement to the SDR needed to account for solar activity at the time of the measurements relative to that for the Day One solar spectrum.

The OMPS-NM and -NP measurements are processed into total column ozone and ozone profile products in near-real-time (NRT) at the NOAA Interface Data Processing Segment (IDPS)and distributed for use in numerical weather models and to assist in forecasting daily ultraviolet (UV) Index values. They are also processed off-line with other retrieval algorithms as a first step in the process of incorporating them into long-term ozone climate data records (CDRs). This paper will discuss results for both types of products but will emphasize the operational ones. The OMPS-LP measurements are processed into ozone profile products by the NASA S-NPP Science Team. The OMPS-LP algorithms are moving toward implementation in the NOAA operations but that topic is not covered in this paper.

2. Ozone Retrieval Algorithms

The OMPS measurements are used to generate estimates of atmospheric ozone in both operational and off-line systems. This paper will concentrate on the on the products from the NOAA IDPS derived from the OMPS-NM and NP measurementsbut will also present some information on some preliminary results using the Version 8 total ozone and profile ozone algorithms to generate climate data records from the OMPS-NM and NP taking place at NASA and NOAA. A brief introduction of the algorithms appears below. More detailed descriptions of the IDPS algorithms can be found in JPSS Algorithm Theoretical Basis Documents (ATBDs), Operational Algorithm Documents (OADs) and Data Format Control Books (DFCB) available at the S-NPP Library:npp.gsfc.nasa.gov/science/documents.html.

A description of research algorithms for the OMPS Limb Profiler is given inRaultandLoughman[2013].

2.1. Nadir Mapper Total Column Ozone

The spectral measurements from the OMPS-NM of the radiances scattered by the Earth’s atmosphere are used to generate estimates of the total column ozone. The IDPS algorithm uses ratios of Earth radiance to Day 1 Solar irradiance measurements at triplets of wavelengths to obtain estimates of the total column ozone, effective reflectivity, and the wavelength dependence of the reflectivity as affected by aerosols. [The Day 1 Solar spectra are a set of spectra used in the algorithm to compute the radiance/irradiance ratios. The algorithm/processing initially used a set of pre-launch estimates for these and then after real solar measurements were taken new estimates were made (system updates in 6/2012 for the OMPS NM and 7/2012 for the OMPS NP). The working diffuser is used every two weeks and the reference diffuser is used every six months to make new measurements. So far the reference diffuser measurements have shown little or no changes above 290 nm and changes from -0.1%/year to -0.5/year growing larger in magnitude from 290 nm to 250 nm. The processing system has daily values for Earth Calibration Factors that can be used to adjust for instrument throughput changes relative to the Day 1 values but they have not yet been activated. More information on the instruments performance is in the companion papers.] Table values computed for a set of standard profiles, cloud heights, latitudes and solar zenith angles are interpolated and compared to the measured top-of-atmosphere albedos. The triplets combine an ozone insensitive wavelength channel (at 364, 367, 372 or 377 nm) to obtain cloud fraction and reflectivity information, with a pair of measurements at shorter wavelengths. The pairs are selected to have one “weak” and one “strong” ozone absorption channel. The hyperspectral capabilities of the sensor are used to select multiple sets of triplets to balance ozone sensitivity across the range of expected ozone column amounts and solar zenith angles. The "strong" ozone channels are placed at 308.5, 310.5, 312.0, 312.5, 314.0, 315.0, 316.0, 317.0, 318.0, 320.0, 322.5, 325.0, 328.0, or 331.0 nm. They are paired with a longer “weak” channel at 321.0, 329.0, 332.0, or 336.0 nm. The ozone absorption cross-sections decrease from 3 (milli-atm. cm)-1 to 0.3 (milli-atm. cm)-1 over the range of “strong” wavelengths. Typical ozone columns range from 100 Dobson Units (1 DU = 1 milli-atm-cm) to 600 DU.

The Multiple Triplet algorithm is applied twice for each FOV. This was done to resolve the “Who goes first?” quandary created by the desires to use information from other sensors in the retrieval algorithms, e.g., OMPS wanted to use the Cross-track Infrared Sounder (CrIS) temperature profile estimates, and CrIS wanted to use the OMPS ozone estimates. The “1st Guess” OMPS-NM products use climatological or forecast fields for surface reflectivity and pressure, snow/ice coverage, cloud optical centroid depth, and atmospheric temperature. Theyuse internally calculated estimates of cloud fractions and effective reflectivity from measurements at non-ozone absorbing UV wavelengths. This product is sometimes called the Total Ozone Intermediate Product (TOZ IP).

The 2nd Pass or EDR OMPS products use snow/ice coverage from the Visible Infrared Imaging Radiometer Suite (VIIRS) near-real-time products and temperature profiles from CrIS products. Both products use internally calculated estimates of cloud fractions and effective reflectivity from measurements at non- or weakly absorbing ozone wavelengths. This second product is sometimes called the Total Ozone Environmental Data Record (TOZ EDR). As we will show, both applications of the algorithm are performing well but have room for improvement.

It was originally planned to use IR measurements to provide the cloud top pressure data for the EDR product but with the development of UV-measurement-based estimates by the EOS Aura Ozone Monitoring Instrument (OMI) Science Team as described in Vasilikov et al.[2008] these were found to often (e.g., for thin cirrus) lead to errors as the IR optical cloud tops would be found at a lower pressure than the UV optical cloud tops. Both OMPS total ozone products are currently using a climatology of UV cloud optical centroids compiled from five years of OMI data. Future plans are to include direct calculation of UV cloud optical centroid pressures from the OMPS measurements.

The total ozone product files contain both Multiple Triplet and Heritage Version 7 Triplet Total Column Ozone estimates. See McPeters et al., [1996] for information on the Version 7 algorithm. The heritage Version 7 products use the 318, 331 and 364 nm channels in a single triplet. Given the current state of the calibration, each triplet will have its own small biases. We are working on soft calibration adjustments to remove the inter-channel biases and homogenize the multiple triplet results. The nice thing about the Version 7 product is that its behavior is only affected by the relative calibration of the three channels in its single triplet. Its weakness is that this triplet is not ideal under all viewing conditions, particularly for high ozone amounts at large solar zenith or satellite viewing angles.

The Version 8 total ozone algorithm used for reprocessing is described inBhartia and Wellemeyer (2002).

2.2. Nadir Profiler

The spectral measurements from the OMPS Nadir Profiler and Nadir Mapper of the radiances scattered by the Earth’s atmosphere are used to generate estimates of the ozone vertical profile along the orbital track. The algorithms currently use ratios of Earth radiance to Solar irradiance at a set of 12 wavelengths (at approximately 252, 274, 283, 288, 292, 298, 302, 306, 313, 318, 331 and 340 nm) with the shortest eighttaken from the Nadir Profiler and the longest four from the Nadir Mapper to obtain estimates of the total column ozone, effective reflectivity, and the ozone vertical profile in 12 Umkehr Layers. (The 12 Umkehr layers boundaries are at:[0,.25,.50,.99,1.98,3.96,7.92,15.8,31.7,63.3,127,253,1013] hPa.)The radiances for the four longer wavelengths are obtained from the 25 Nadir Mapper FOVs co-located with a single Nadir Profiler FOV. The IDPS ozone profile EDR product is made using an implementation of the Version 6 Solar Backscatter Ultraviolet instruments (SBUV/2) algorithm [Bhartia et al. 1996]. The longer channel radiance/irradiance ratios are used to generate estimates of the total column ozone and scene effective reflectivity. This total column ozone estimate is combined with a power law ozone profile in the upper layer from the shorter channelsto generate a first guess ozone profile that becomes the A Priori for a maximum likelihood ozone profile retrieval using the ratios for the seven shortest wavelengths (currently omitting the 252 nm channel); adding the 313 nm channel at high solar zenith angles (SZA). Additional information is in the OMPS Nadir Profile Algorithm Theoretical Basis and Operational Algorithm Description Documents, and a volume of the Common Data Format Control Book. The Version 8 Ozone Profile algorithm used for reprocessing and operationally at NOAA for the SBUV/2 is described in Bhartia et al. [2013]. The Version 6 ozone profile is reported as Dobson Units (milli-atm-cm) in Umkehr Layers for 12 layers – with the bottom two layers, layers 0 and 1, combined, and the top layer extending upward including layers 12 and above. It is also reported as ozone mixing ratios at 19 pressure levels. This latter product is obtained by taking the derivative of a spline fit of the cumulative layer ozone amounts.

3. Products and internal consistency

The OMPS total ozone and ozone profile products from the operational system are available as provisional-release data sets through links at .

3.1. Total Column Ozone

The OMPS-NM total column ozone product provides estimates over the full sunlit Earth of total column ozone, effective reflectivity and UV absorbing aerosols (an aerosol index) each day. The measurements are binned into 35 cross-orbital-track fields of view (FOVs) on-board the spacecraft with each FOV using a specific fixed set of CCD pixels. The performance requirements for the Total Ozone EDR are given in Table 1. As can be seen, the requirements are stratified by ozone amount. There is an additional long-term requirement that reprocessed products for climate data records should be stable at the 1%/decade level. The initial evaluation of the products in this sectionlooks at the values for the retrieval quantities relative to those expected from past experience as well as the cross-track consistency of the results as internal checks.

One of the initial ways to examine the performance of the products is to see if they match the expected range and distribution of values. Figures 1.a, 1.b and 1.c provide a typical example of this check for the primaryOMPS-NM total column EDR algorithm products. They show false color global maps of (a) total column ozone, (b) effective reflectivity and (c) an aerosol index for April 3, 2013 from the IDPS EDR total ozone products. Maps for other days for the last 18 months – and for other monitoring products – are available for viewing at the NOAA Satellite Integrated Calibration/ Validation System (ICVS) web site at

Figure 1.a is for total column ozone. The colors show different levels of ozone in Dobson Units (milli-atm-cm). The large amounts in the Northern Hemisphere are expected at this time of year. The black area around the South Pole is a region of polar night where there is no sunlight to make the OMPS measurements.

Figure 1.b is for the effective reflectivity. The colors show varying reflectivity in percent. The range from close to 0% over cloud-free land (e.g.,, the Sahara desert) to close to 100% for bright clouds and snow/ice covered surfaces (e.g., Antarctica) is as expected. The EDR product derives this estimate from the longest wavelength of each triplet where the ozone absorption is negligible.

Figure 1.c is for an absorbing aerosol index. The colors show different levels of the index computed as a measurement residual for the 364 nm channel using the reflectivity estimate from the 331 nm channel. While some features are expected (e.g., dust over the Sahara) others, such as the North/South bands in the mid-Pacific are not. Some small features over the open ocean near the Equator are produced by sun glint but the large North/South features result from cross-track biases between the two channels and are discussed later in this section.