DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING 4. Satellite Validation Principle C o r r e l a t i v e D a t Day 4 Lecture 2 Instrument intercomparison – Paul Simona 1 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Atmospheric Remote Sensing Measurements • Atmosphere is continuously changing in time and space. => No repeated measurements of the same quantity. • Radiation field measurements are direct, all other are indirect • Measurements probe large atmospheric volume => Large averaging and validation by in situ measurements difficult Courtesy Erkki Kyrola Day 4 Lecture 2 Instrument intercomparison – Paul Simon 2 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Atmospheric Satellite Sensors We launch a satellite sensor for dedicated purposes: Meteorology, dynamical tracer, surface UV monitoring; Global climatology; Montreal and Kyoto Protocol related issues; Atmospheric processes: polar chemistry, etc.; Tropospheric issues like pollution, biomass burning, oxidizing capacity…; Radiative Transfer and Chemical Transport modelling. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 3 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Ideally, the observations of atmospheric constituents must not be dependent on: ¾ the atmospheric temperature; ¾ the abundance of other species; ¾ the Sun elevation; ¾ the presence of clouds; ¾ the instrument degradation (aging); ¾ etc… Day 4 Lecture 2 Instrument intercomparison – Paul Simon 4 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles First issue: Remote sensing output is affected by: Instrument degradation; Calibration uncertainties; Errors/assumptions on retrieval model (forward + inverse): radiative transfer codes, spectroscopic databases, atmospheric profile databases, surface albedo, treatment of clouds and aerosols. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 5 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite validation principles Therefore: ¾ Validation is required to confirm error budgets derived from theoretical and laboratory studies, and identify new error sources. ¾ Quantitative validation must take into account both satellite and correlative data error sources. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 6 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Second issue: Remote sensing does not provide a direct measure of the number density, but: Earth radiance and solar irradiance measurements Horizontal resolution Latitude/time sampling The [measurement] + [retrieval algorithm] system is characterised by weighting functions determining altitude range, sensitivity, vertical resolution of the retrieved information Day 4 Lecture 2 Instrument intercomparison – Paul Simon 7 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Therefore: ¾ Validation must characterise the real information content coming from the measurement, including sampling and smoothing aspects, and independency w.r.t. databases and assumptions. ¾ Satellite and ground-based data give a differently smoothed/sampled/truncated perception of the ozone field. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 8 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Third issue: Atmospheric ozone exhibits 9 Spatial structures; 9 Temporal variability at a hierarchy of scales; 9 Strong correlations with temperature, altitude/pressure, dynamics, etc. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 9 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Therefore: ¾ It is not a well mixed, homogeneous, like laboratory sample; ¾ No linearity; ¾ Differences in ozone field perception make comparisons and their interpretation difficult. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 10 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Conclusion: Proper validation is highly instrumental driven in: 9 Determining if, how and to what extent satellite data can meet the dedicated objectives 9 Pointing to defiances in calibration and retrieval algorithms 9 Improving data products Day 4 Lecture 2 Instrument intercomparison – Paul Simon 11 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation Principles Validation goes well beyond a simple comparison exercise, in scope and in difficulty; ideally it should combine both qualitative and quantitative correlative studies with information content studies. Scientific/operational purposes must serve as a baseline. A few comparison pairs at a few stations during a limited campaign are by far not sufficient. Day 4 Lecture 2 Instrument intercomparison – Paul Simon 12 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING GOME GDP 2.7 versus Dobsons (4 years) > +3% < -5% Lambert et al., > +3% ESA TN, ESA TN, < -6% > +5% 2002 However, annual means concluded to an excellent agreement ! Day 4 Lecture 2 Instrument intercomparison – Paul Simon 13 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING T dependence of ozone cross-section GOME versus Dobsons and Brewers GDP 3.0 GDP 4.0 Day 4 Lecture 2 Instrument intercomparison – Paul Simon 14 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING T dependence of ozone cross-section TOMS versus Dobsons and Brewers Day 4 Lecture 2 Instrument intercomparison – Paul Simon 15 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Solar Zenith Angle dependence 40 Tropic of Capricorn Northern Mid-latitudes 30 60° North Arctic Polar Circle Northern Polar Latitudes 20 10 0 GDP 2.7 / 3.0 / 4.0 -10 -20 GDP 1.20 -30 SZA Dependence of GOME v2.0 Total Ozone 20 30w.r.t. 40 SAOZ 50 Network 60 Observations 70 80 90 100 Solar zenith(Jul angle - Nov of GOME1996) (deg) 20 15 GDP 2.0 10 5 0 -5 (GO S O )/S O % -10 -15 All latitudes excepted Antarctica Vertical error bars: standard deviation (2σ) -20 20 30 40 50 60 70 80 90 100 Solar zenith angle of GOME [deg.] Day 4 Lecture 2 Instrument intercomparison – Paul Simon 16 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Ozone Profile Validation Similar problems as with ozone column validation plus: 9 Importance of absolute radiometric calibration; 9 Polarization aspects (instrument + atmosphere); 9 Vertical smoothing issues; 9 Retrieved value is a mix of measured information and a priori information (first guess, constraints); 9 Geolocation and time mismatches; 9 Upper stratosphere: diurnal variation of ozone, … Day 4 Lecture 2 Instrument intercomparison – Paul Simon 17 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Collocation Are we trying to integrate apples and bananas? What does "collocation" mean? Day 4 Lecture 2 Instrument intercomparison – Paul Simon 18 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Error Budget of a Comparison Error covariance matrix: Five covariance contributions 1. Measurements errors 2. Errors associated with measurement parameters 3. Retrieval parameter errors 4. Vertical smoothing error 5. Horizontal smoothing error (or “collocation” errors) S= SM + SB + SSA + SSV + SSH Day 4 Lecture 2 Instrument intercomparison – Paul Simon 19 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING ErrorBudget of a Comparison Dependent on: – technique, – constituent, – atmospheric state (variability, profile shape, temperature, surface …) … –andintended use ! Day 4 Lecture 2 Instrument intercomparison – Paul Simon 20 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING OZONE Profile Validation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 21 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Ozone Profile Validation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 22 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Ozone Sondes & Lidar Validation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 23 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Ozone LIDAR Validation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 24 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Day 4 Lecture 2 Instrument intercomparison – Paul Simon 25 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Day 4 Lecture 2 Instrument intercomparison – Paul Simon 26 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Day 4 Lecture 2 Instrument intercomparison – Paul Simon 27 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation by Microwave Radiometer SOMARA • Averaging kernel smoothing has been applied • Horizontal distance < 800 km from SOMORA in Payerne • Time difference < 1h between ground and satellite data • Time intervals of satellites data are quite different Day 4 Lecture 2 Instrument intercomparison – Paul Simon 28 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Satellite Validation by Microwave Radiometer good agreement of all instruments at altitudes < 45 km SOMORA Day 4 Lecture 2 Instrument intercomparison – Paul Simon 29 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING MIPAS Ozone Validation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 30 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING TemperatureValidation Day 4 Lecture 2 Instrument intercomparison – Paul Simon 31 DRAGON ADVANCED TRAINING COURSE IN ATMOSPHERE REMOTE SENSING Validation of MIPAS Temperature