Earth Observing System (EOS) Aura Science Data Validation Plan Calibration & Modeling Aircraft Ground-based & Balloon Data Campaigns Satellite Data Version 1.0 July 12, 2001 EOS Aura Science Data Validation Plan Executive Summary I. The Aura Mission The Aura satellite is scheduled to be launched in 2003 in a sun-synchronous polar orbit for a nominal mission of five years. The four Aura instruments are: the High Resolution Dynamics Limb Sounder (HIRDLS), measuring infrared emission profiles from high resolution atmospheric limb scans behind Aura; the Microwave Limb Sounder (MLS), obtaining limb emission profiles ahead of the satellite; the Ozone Monitoring Instrument (OMI), a nadir- viewing UV/VIS imaging spectrometer with high spatial resolution; the Tropospheric Emission Spectrometer (TES), a Fourier Transform infrared spectrometer measuring in both the nadir and the limb mode behind Aura. Section 2 of this document gives the Aura science goals, a description of the instruments and measurement characteristics. The top-level objectives are to resolve the following science questions: • Is the ozone layer changing as expected? • Do we understand the transport of gases within the stratosphere and between the stratosphere and troposphere? • What are the sources and distributions of tropospheric pollutants? • What are the roles of upper tropospheric water vapor, aerosols, and ozone in climate change? The main products from Aura will be: (1) Stratospheric profiles of temperature, O3, H2O, OH, HO2, CH4, CO, HCN, CH3CN, N2O, HNO3, NO, NO2, N2O5, HCl, ClO, ClONO2, HOCl, CF2Cl2, CFCl3, BrO, and aerosol extinction; (2) Tropospheric profiles of temperature, O3, H2O, CH4, CO, and HNO3; upper tropospheric observations of NO, NO2, and HCN; tropospheric column densities of O3 and NO2. (3) Column densities of O3, NO2, HCHO, BrO, OClO. (4) aerosol optical thickness. (5) cloud information. (6) volcanic SO2. Section 3 provides more details about these products and their expected uncertainties. II. Summary of Aura Plans for Pre-launch Activities Three major pre-launch activities that are necessary for successful (post-launch) validation of Aura products are: (1) Instrument calibration, (2) Algorithm testing, and (3) Compilation of spectroscopic data and other databases. These are discussed in section 4. II.1 Instrument Calibration Instrument calibration is closely tied to the continuing hardware development and testing of the Aura instruments. Each instrument will have detailed specific issues and schedules to follow. Pre-launch instrument and Project reviews and reports provide the means to assess the progress of the calibration plans that are briefly discussed (section 4.1). i II.2 Algorithm Testing Pre-launch algorithm testing is discussed in section 4.2. The success of this testing directly impacts the quality of processed data after launch. Current test plans are summarized for each instrument team’s algorithm. Where feasible, algorithms will be tested on data obtained by earlier satellite instruments. Algorithm mathematical approaches and some accuracy estimates are given in the Algorithm Theoretical Basis Documents. The Algorithm Working Group will guide some of the common activities (e.g., the use of a common model atmosphere for simulations and end-to-end testing), but much of the detailed work rests within each instrument team. Updates regarding algorithm status are ongoing and planned on a regular basis before the launch-ready software deliveries. II.3 Spectroscopic Data and Other Databases Databases of interest to the Aura instrument teams are identified, along with needs for new spectroscopic data (section 4.3). Since spectroscopic data generally come from outside the instrument teams, such needs were recently included as part of a NASA Research Announcement towards validation of data from the Aura and Aqua platforms. Through this and similar efforts, it is expected that many of the desired improvements in these databases will be met before the Aura launch. However, some important items (notably, information on the challenging HNO3 infrared bands of relevance to both HIRDLS and TES, and on O2-O2 visible absorption cross sections for OMI) will require more attention in order for the satellite measurement accuracy requirements to be met. As each instrument team stays abreast of the uncertainties that remain in these databases, proper estimates of expected post-launch accuracy in the retrieved geophysical products can be made; this is a crucial and time consuming aspect of the validation assessments. Other pre-launch activities currently underway include the gathering and/or development of data sets for use in the retrievals and/or simulations (climatology, operational meteorological data, or model values), coincidence predictor software, as well as gathering of other databases such as surface albedo and emissivity. II.4 Models Atmospheric models have several pre-launch applications to Aura validation. Constituent fields from atmospheric models will be used in synthetic data needed for algorithm testing. These constituent fields will also be used to develop strategies to obtain optimal information from comparisons of correlative observations with Aura measurements, especially in the upper troposphere and lower stratosphere where temporal and spatial scales of variability are much smaller than in the middle and upper stratosphere. Model fields will be used to develop quantitative requirements for coincidence criteria and also to develop statistical methods of comparison. III. Summary of Aura Plans for Post-Launch Activities The following paragraphs summarize the plans for validation activities following Aura launch as given in more detail in section 5. This plan will evolve and will include plans for correlative data location/extraction, formats, and data exchange protocols (section 6), as well as coincidence predictor software (also mentioned in section 4). Some of the specifics of this planning will have to await further definition of the investigations to be selected in support of Aura validation and science. ii III.1 Aura Measurements and Validation Overview Tables I.1, I.2, and I.3 summarize the measurements needed for validation of stratospheric profiles, tropospheric profiles, and column densities and other needs, respectively. Expected satellite, ground-based, and sonde data sources and opportunities are listed generically (for more details, see Table 5.3), with columns for satellite and ground-based data indicating expected amounts and quality/extent of match with Aura data. A priority column (with 1 for high, 2 for medium, 3 for lower priority) is used to indicate correlative data need as well as scientific importance of the Aura measurements (based on section 5.2.3.2). More details for each product can be found in section 5.2.3.3. Although a significant number of tropospheric chemistry campaigns have occurred in the 1990’s, there are no global data bases for most tropospheric constituents. Validation activities for tropospheric data are necessary over a broad range of latitudes and seasons. III.2 Aerosols and Clouds Besides the scientific interest in aerosols and clouds, these particles can affect the retrievals of other Aura products in the lower stratosphere and troposphere. OMI is sensitive to light- absorbing lower tropospheric particles (desert dust, particles from fires); HIRDLS and TES will sense stratospheric sulfate, polar stratospheric cloud, and upper tropospheric cirrus particles; the MLS experiment senses large particles (larger than 100 µm). A key validation source for the OMI experiment will be the aerosol optical thickness and single scattering albedo values measured by the AERONET set of ground based instruments. The primary measurements desired for HIRDLS and TES are particle size measurements of sulfate, PSCs, and upper tropospheric cirrus, and lidar measurements of aerosol spatial distributions, as well as other satellite observations of the extinction of the three types of particles. Correlative tropospheric aerosol composition information would also be useful. For the MLS cloud ice and OMI cloud products, the primary validation will use data from the Earth System Science Pathfinder (ESSP) Project mission CloudSat and ESSP3 (formerly PICASSO-CENA), but for MLS campaigns including cloud measurements of large ice particles are desirable. Measurements of the composition of stratospheric PSCs would allow us to relate satellite spectral information to composition. III.3 Column Densities The most important, currently unmet, validation need for OMI column densities is for tropospheric NO2 under polluted as well as clean conditions; tropospheric ozone column densities are also desirable, as part of Aura-related campaigns. Under polluted NO2 conditions, column and profile information in the lower troposphere is essential for the column density validation. Choices for this validation requirement are currently limited. The ozone column measurement, also high priority, can be validated by Brewer Dobson instruments, integrating sonde measurements or by comparison to other satellite measurements (i.e. TOMS, GOME, SCIAMACHY). Again, not many of these instruments are located in very polluted areas, thus additional measurements are needed. An aircraft campaign (e.g., with a UV-VIS DOAS-type instrument aboard) in which measurements of tropospheric and stratospheric profiles and column densities of NO2 and O3 are performed, can be used for these purposes (see also III.8 and III.9). iii Table I.1. Aura stratospheric