K. Chance, X. Liu, C. Chan Miller, G. González Abad, G. Huang, C. Nowlan, A. Souri, R. Suleiman, K. Sun, H. Wang, L. Zhu, P. Zoogman, J. Al-Saadi, J. -C. Antuña-Marrero, J. Carr, R. Chatfield, M. Chin, R. Cohen, D. Edwards, J. Fishman, D. Flittner, J. Geddes, M. Grutter, J. Herman, D. Jacob, S. Janz, J. Joiner, J. Kim, N. Krotkov, B. Lefer, R. Martin, O. Mayol-Bracero, A. Naeger, M. Newchurch, G. Pfister, K. Pickering, R. Pierce, C. Rivera Cárdenas, A. Saiz-Lopez, W. Simpson, E. Spinei, R. J. Spurr, J. Szykman, O. Torres, J. Wang
The NASA/Smithsonian Tropospheric Emissions: Monitoring of Pollution (TEMPO; tempo.si.edu) satellite instrument will measure atmospheric pollution and much more over Greater North America at high temporal resolution (hourly or better in daylight, with selected observations at 10 minute or better sampling) and high spatial resolution (10 km2 at the center of the field of regard). It will measure ozone (O3) profiles (including boundary layer O3), and columns of nitrogen dioxide (NO2), nitrous acid (HNO2), sulfur dioxide (SO2), formaldehyde (H2CO), glyoxal (C2H2O2), water vapor (H2O), bromine oxide (BrO), iodine oxide (IO), chlorine dioxide (OClO), as well as clouds and aerosols, foliage properties, and ultraviolet B (UVB) radiation. The instrument has been delivered and is awaiting spacecraft integration and launch in 2022. This talk describes a selection of TEMPO applications based on the TEMPO Green Paper living document (http://tempo.si.edu/publications.html).
Applications to air quality and health will be summarized. Other applications presented include: biomass burning and O3 production; aerosol products including synergy with GOES infrared measurements; lightning NOx; soil NOx and fertilizer application; crop and forest damage from O3; chlorophyll and primary productivity; foliage studies; halogens in coastal and lake regions; ship tracks and drilling platform plumes; water vapor studies including atmospheric rivers, hurricanes, and corn sweat; volcanic emissions; air pollution and economic evolution; high-resolution pollution versus traffic patterns; tidal effects on estuarine circulation and outflow plumes; air quality response to power blackouts and other exceptional events.
Ultraviolet irradiance (UV from 290 nm to 325 nm) reaching the earth's surface has significantly increased at all latitudes
except the equatorial zone since 1979. The annual average increase was caused by a corresponding decrease in ozone
amount from1979 to 1998. After 1998, mid-latitude annual average ozone amounts and UV irradiance levels have been
approximately constant. Cloud plus aerosol changes over the period from 1979 to 2008 have caused significant
moderation of the clear-sky UVB trends based on a preliminary analysis of UV (340 nm) scene reflectivity data from
multiple satellites.
We present first results from the newly developed remote sensing instrument CLEO (CLear Sky Observatory). CLEO
consists of a commercially available CCD miniature spectrometer (Hamamatsu C10082CAH) and foreoptics to measure
the global and diffuse solar irradiance. The irradiance is measured through a teflon diffuser. The diffuse irradiance is
obtained moving a 180° metal band in the optical path to block the solar direct beam. CLEO measures simultaneously
UV and Visible radiation from 163nm to 845nm, in steps of 0.3nm with a resolution of 1nm. The spectrometer is
temperature controlled to 10°C to stabilize its optical properties. The dark count is frequently measured using a
motorized four positions filterwheel with an opaque disc at one position that acts as a shutter used to block the light
input. The system automatically adjusts the integration time to optimize the signal-to-noise. Another difference to
previous shadowband instruments is that CLEO moves the shadowband over the whole hemisphere instead of just a few
positions in and around the sun's direction. This has the advantage of simplifying the installation procedure and solves
the problem with the shadow only partially covering the diffuser due to instrument misalignment.
We evaluate the feasibility of a balloon-borne nulling interferometer to detect and characterize an exosolar planet and the
surrounding debris disk. The existing instrument consists of a three-telescope Fizeau imaging interferometer with thre
fast steering mirrors and three delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine
pointing. A compact visible nulling interferometer would be coupled to the imaging interferometer and in principle,
allows deep starlight suppression. Atmospheric simulations of the environment above 100,000 feet show that balloonborne
payloads are a possible path towards the direct detection and characterization of a limited set of exoplanets and
debris disks. Furthermore, rapid development of lower cost balloon payloads provide a path towards advancement of
NASA technology readiness levels for future space-based exoplanet missions. Discussed are the BENI mission and
instrument, the balloon environment and the feasibility of such a balloon-borne mission.
Column aerosol absorption properties in the visible wavelengths are measured routinely in worldwide
locations by NASA AERONET network (http://aeronet.gsfc.nasa.gov), while similar optical properties in UV
can be derived from diffuse and global irradiance measurements measured with Multifilter Rotating
Shadowband Radiometer (MFRSR) instruments of the USDA UV-MFRSR network
(http://uvb.nrel.colostate.edu). To enable direct comparisons between the two techniques, we have modified
our UV-MFRSR by replacing standard 300nm filter with 440nm filter used in AERONET network. The
modified UV/VIS-MFRSR has been mostly deployed at AERONET calibration site at NASA GSFC in
Greenbelt, MD, but also at number of field campaigns. While the UV-MSFRSR instrument is highly
susceptible to calibration drifts, these drifts can be accurately assessed using co-located AERONET direct-sun
AOT data. In 2006 quartz dome has been installed atop the MFRSR diffuser, which stabilized calibration
drifts in 2007-2009. After correcting for remaining calibration changes, the AOT and single scattering albedo
(SSA) at the UV wavelengths can be accurately inferred by fitting the measurements of global and diffuse
atmospheric transmittances with the forward RT model at each UV-MFRSR spectral channel. Derived AOT
and SSA at common wavelength 440nm by two different techniques are generally in good agreement. We
also found that SSA becomes smaller in the UV wavelengths and has strong wavelength dependence across
blue and near-UV spectral range. The measured enhanced UV absorption might suggest the presence of
selectively UV absorbing aerosols. High spectral resolution SSA measurements in UV-VIS wavelengths are
called for.
Long-term ground-based UV radiometers and satellite UV spectrometers have been utilized for detecting trends in UV
radiation and for establishing its climatology. The aim of this work is to compare noon erythemal (CIE) UV irradiance
data from NASA Total Ozone Mapping Spectrometer (TOMS) with ground-based measurements from a Brewer
spectrophotometer. The Brewer instrument is located at the Atmospheric Sounding Station "El Arenosillo" (ESAt) in
Huelva, Southwestern Spain. ESAt, with a high number of cloud-free days per year, is particularly suitable for
atmospheric-radiation studies and satellite validation. The period of study covers the years 2000 to 2004. The effect of
clouds and aerosols on the satellite vs ground-based bias is evaluated under different atmospheric conditions regarding
aerosol load and cloudiness. It is found that under all sky conditions TOMS overestimates the noon CIE irradiance about
8%. This bias is even higher (about 12%) for cloud-free days, showing statistically significant correlation with the
aerosol optical depth at 440 nm as measured by a co-located CIMEL-AERONET sunphotometer. However, for thick
clouds (high TOMS reflectivity) the bias becomes negative. Regarding aerosols, the bias increases as the aerosol load
increases, showing the highest values during dust events. All these facts suggest the need to correct the TOMS UV
products mainly under dust conditions.
O3, SO2 and NO2 vertical column amounts and aerosol optical depths at 18 wavelengths from 303 to 363nm were measured daily for the past two years by using a Brewer MK3 double spectrometer in direct-sun mode. The algorithms used are described and compared to the standard algorithm. For O3 and SO2 the standard algorithm was modified by using all 6 measured wavelengths instead of only 4 or 5 and by including a correction for the diffuse irradiance entering the instrument's field of view. This reduces the statistical error of the retrievals by 40% and 50%, respectively, for O3 and SO2. The NO2 retrievals are based on a spectral fitting technique using wavelengths between 349 and 363nm. A 'Bootstrap method' has been developed to calibrate the Brewer for NO2 measurements. This method selects data with lowest NO2-amounts and uses them to derive the needed extraterrestrial solar spectrum. We discuss possible reasons why an intent to apply to same technique for deriving total HCHO columns failed. The main advantage of direct sun methods compared to Differential Optical Absorption Spectroscopy DOAS is that the uncertainty in the air mass factor is significantly smaller. We think that a better correction for the diffuse irradiance entering the instrument's field of view will further improve the retrievals, especially in the low wavelength range (303 to 320nm) used for O3 and SO2.
A significant database of simultaneous measurements of NO2 column amounts and aerosol optical properties has recently become available that permits partitioning between aerosol and gaseous absorption. The aerosol column absorption optical thickness, (AAOT) was inferred from the measurements of global and diffuse atmospheric transmittances by a UV-Multifilter Rotating Shadowband radiometer (UV-MFRSR), calibrated using AERONET CIMEL sun-sky radiometers. The NO2 column amounts were measured using a double-Brewer MK III spectrometer (#171) operated in direct-sun mode using a new 6-wavelength retrieval algorithm. Ancillary measurements of column particle size distribution and refractive index in the visible wavelengths (by AERONET sun-sky almucantar inversions), ozone (by Brewer) and surface pressure constrained the forward radiative transfer model input, so that a unique solution for AAOT was obtained in each UV-MFRSR spectral channel. In fall-winter months with typically dry conditions and low aerosol loadings, the NO2 absorption represented a significant source of error in aerosol absorption measurements. This was confirmed by UV-MFRSR AAOT retrievals at 325nm, where the NO2 absorption cross-section is only half the value at 368nm. Thus, the NO2 correction not only reduces AAOTs obtained from traditional aerosol remote sensing techniques (shadowband or Cimel sunphotometer), but also is capable of changing the spectral dependence of aerosol absorption, which could result in an incorrect interpretation of aerosol composition. To further confirm these findings, a new UV-MFRSR instrument was modified by adding a 440 nm channel to provide spectral overlap with AERONET AAOT inversions in the visible wavelengths.
We analyzed long-term variations of UV irradiance 300-380 nm over Moscow 55.7N, 37.5E since 1968 using a complex dataset that includes ground-based UV measurements, UV retrievals from two satellites, and the results of a previously developed empirical model. Long-term interannual changes of UV irradiance, 300-380nm, during 1968-2003 show the absence of any linear trends although an increase is detected in the late 90-s due to cloud amount and aerosol content decrease. The ground-based data are compared with UV satellite retrievals from two independent methods as well as with the results of an empirical model that accounts for the physical dependence of UV on cloud parameters (amount and optical thickness), surface albedo, total ozone, and aerosol properties of the atmosphere. UV datasets over Moscow obtained from different satellite instruments: from the Total Ozone Mapping Spectrometer (TOMS) data (version 8) since 1979 and from METEOSAT/MVIRI since 1984. The original METEOSAT processor, using visibility observations at a nearby meteorological station to quantify the aerosol load, leads to a significant underestimation of the UV daily doses (-23% in warm period and -31% in cold period). Substituting the visibility observations by in situ monthly mean aerosol optical depth improves significantly the agreement in both warm and cold periods (respectively, -9% and -10%) but the bias still remains. The difference between TOMS UV retrievals and ground-based data has different signs in warm (+6%) and cold (-15%) periods. Applying off-line absorbing aerosol correction in TOMS UV retrievals eliminates the positive bias in warm period. The negative bias during the cold period can be due to the application of minimum Lambertian effective reflectivity (MLER) approach to determine the surface albedo especially in conditions with non stable snow cover (end of February- March, and November-December). Model reconstruction of UV variability demonstrates high correlation with aerosol corrected satellite UV retrievals (0.83-0.94) as well as with ground data (0.82) during warm period. During cold months the correlation between satellite UV retrievals and ground-based measurements is much worse.
Radiative transfer calculations of UV irradiance from total ozone mapping spectrometer (TOMS) satellite data are frequently overestimated compared to ground-based measurements because of the presence of undetected absorbing aerosols in the planetary boundary layer. To reduce these uncertainties, an aerosol UV absorption closure experiment has been conducted at the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) site in Greenbelt, Maryland, using 17 months of data from a shadowband radiometer [UV-multifilter rotating shadowband radiometer (UV-MFRSR), U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Network] colocated with a group of three sun-sky CIMEL radiometers [rotating reference instruments of the NASA Aerosol Robotic Network (AERONET)]. We describe an improved UV-MFRSR on-site calibration method augmented by AERONET-CIMEL measurements of aerosol extinction optical thickness (a) interpolated or extrapolated to the UV-MFRSR wavelengths and measurement intervals. The estimated a is used as input to a UV-MFRSR spectral-band model, along with independent column ozone and surface pressure measurements, to estimate zero air mass voltages V0 in three longer wavelength UV-MFRSR channels (325, 332, 368 nm). Daily mean V0, estimates and standard deviations are obtained for cloud-free conditions and compared with the on-site UV-MFRSR Langley plot calibration method. By repeating the calibrations on clear days, relatively good stability (±2% in V0) is found in summer, with larger relative changes in fall-winter seasons.
Compared to the visible spectral region, very little is known about aerosol absorption in the UV. Without such information it is impossible to quantify the causes of the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report results of a 17-month aerosol column absorption monitoring experiment conducted in Greenbelt, Maryland, where the imaginary part of effective refractive index k was inferred from the measurements of direct and diffuse atmospheric transmittances by a UV-multifilter rotating shadowband radiometer [UV-MFRSR, U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Network]. Colocated ancillary measurements of aerosol effective particle size distribution and refractive index in the visible wavelengths [by CIMEL sun-sky radiometers, National Aeronautics and Space Administration (NASA) Aerosol Robotic Network (AERONET)], column ozone, surface pressure, and albedo constrain the forward radiative transfer model input, so that a unique solution for k is obtained independently in each UV-MFRSR spectral channel. Inferred values of k are systematically larger in the UV than in the visible wavelengths. The inferred k values enable calculation of the single scattering albedo , which is compared with AERONET inversions in the visible wavelengths. On cloud-free days with high aerosol loadings [ext(440)>0.4], is systematically lower at 368 nm (368=0.94) than at 440 nm (440=0.96), however, the mean differences (0.02) are within expected uncertainties of retrievals (~0.03). The inferred is even lower at shorter UV wavelengths (325~332=0.92), which might suggest the presence of selectively UV absorbing aerosols. We also find that decreases with decrease in aerosol loading. This could be due to real changes in the average aerosol composition between summer and winter months at the Goddard Space Flight Center (GSFC) site.
We report final results of an aerosol UV absorption closure experiment where a UV-shadow-band radiometer (UV-MFRSR, USDA UVB Monitoring and Research Network) and 4 rotating sun-sky radiometers (CIMEL, NASA AERONET network) were run side-by-side continuously for 17 months at NASA/GSFC site in Greenbelt, MD. The aerosol extinction optical thickness τext, was measured by the CIMEL direct-sun technique in the visible and at two UV wavelengths 340 and 380 nm. These results were used for UV-MFRSR daily on-site calibration and 3-min measurements of τext at 325nm, 332nm and 368nm. The τext measurements were used as input to the radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD)to infer an effective imaginary part of the UV aerosol refractive index, k, by fitting MFRSR measured voltage ratios. Using all cases for cloud-free days, we derive diurnal and seasonal dependence of the aerosol absorption optical thickness, τabs with an uncertainty 0.01-0.02. At our site τabs follows pronounced seasonal dependence with maximum values ~0.07 at 368nm (~0.15 at 325nm) occurring in summer hazy conditions and <0.02 in winter-fall seasons, when aerosol loadings are small. Inferred values of k allow calculation of the single scattering albedo, ω, in UVA and comparisons with AERONET almucantar ω440 retrievals at 440nm. Overall, ω was slightly lower in UV than in the visible: case average <ω368>=0.93 compared to <ω440>=0.95. However, the differences (<ω440 - ω368> ~0.02, rms difference ~0.016) are smaller than uncertainties of both retrievals (δω~0.03). Low <ω368> values are consistent with higher values for imaginary refractive index, k: <k368> ~0.01 compare to <k440> ~0.006. However, mean differences in k (<k368-k440>~0.004) were only slightly larger than AERONET retrieval uncertainty δk ~0.00327. We also found that ω decreases with decrease in τext, suggesting different aerosol composition in summer and winter months. So far, our results do not allow explaining the causes of apparent larger aerosol absorption in UV. Continuing co-located measurements at GFSC is important to improve the comparison statistics, but conducting aerosol absorption measurements at different sites with varying conditions is also desirable.
The polarization sensitivity of a Brewer MKIII double spectrophotometer was measured in the laboratory. We found two major sources of polarization sensitivity. 1) The flat quartz plate as the first optical element alters the polarization state of the transmitted light by Fresnel reflection at oblique incident angles. 2) The internal grating produces almost 100% polarization of the incident light perpendicular to the direction of the ruled grating. The combination of both effects results in a zenith angle (ZA) dependence of the instrument’s sensitivity for unpolarized input such as from Direct Sun measurements. The Brewer is 2% more sensitive at ZA=0° and 10% less sensitive at ZA=80° with respect to normal incidence (ZA=35°). Since the ZA-dependence is independent of wavelength this effect cancels out when calculating wavelength-ratios as used for total ozone retrieval. However the ZA-dependence causes errors when absolute signals at single wavelengths are needed as for aerosol optical depth (AOD) retrievals. Based on our laboratory measurements an overestimation of the Langley extrapolation between 3% and 5% is estimated even at best atmospheric conditions. The ZA-dependence causes 0.025-0.045 overestimation of AOD and an underestimation of the Angstrom exponent. We believe that this effect has not been detected from Brewer AOD-measurements since it is masked by larger uncertainty sources of other nature and AOD-comparisons to other instruments in the short UV-region are rare. Knowing the ZA-dependence it is possible to correct for the ZA-effect. We modified our Brewer by incorporating a depolarizer in its optical path and replacing the flat quartz window by a curved one, so that the input is always at normal incidence, which reduces the ZA-effect.
TOMS UV algorithm is capable of taking into account the scattering aerosols via its scene reflectivity. It also accounts for absorbing aerosols in free troposphere (dust and smoke plumes) via aerosol index correction. On the other hand, the effects of aerosol absorption in the boundary layer are not properly taken into account, because they do not appear as absorbing aerosols in the TOMS AI data (positive AI). This additional error has been claimed to be the reason for the observed positive bias between TOMS derived UV and ground-based measurements. We compared TOMS overpass irradiances against the Brewer measurements in NASA/GSFC site in USA and Thessaloniki, Greece with the main objective of evaluating the effect of absorbing aerosols with the measurements of aerosol optical properties. We found that the bias between TOMS UV and ground-based data depends on the aerosol absorption. In other words, the bias was increasing with the increasing aerosol absorption, τabs. A simple correction to account for this effect is proposed, assuming that the climatology of τabs is known.
KEYWORDS: Sensors, Space telescopes, Telescopes, Mirrors, Digital signal processing, Beam splitters, Interferometers, Wavefronts, Control systems, Prototyping
The Earth Atmospheric Solar-Occultation Imager (EASI) is a proposed interferometer with 5 telescopes on an 8-meter boom in a 1D Fizeau configuration. Placed at the Earth-Sun L2 Lagrange point, EASI would perform absorption spectroscopy of the Earth’s atmosphere occulting the Sun. Fizeau interferometers give spatial resolution comparable to a filled aperture but lower collecting area. Even with the small collecting area the high solar flux requires most of the energy to be reflected back to space. EASI will require closed loop control of the optics to compensate for spacecraft and instrument motions, thermal and structural transients and pointing jitter. The Solar Viewing Interferometry Prototype (SVIP) is a prototype ground instrument to study the needed wavefront control methods. SVIP consists of three 10 cm aperture telescopes, in a linear configuration, on a 1.2-meter boom that will estimate atmospheric abundances of O2, H2O, CO2, and CH4 versus altitude and azimuth in the 1.25 - 1.73 micron band. SVIP measures the Greenhouse Gas absorption while looking at the sun, and uses solar granulation to deduce piston, tip and tilt misalignments from atmospheric turbulence and the instrument structure. Tip/tilt sensors determine relative/absolute telescope pointing and operate from 0.43 - 0.48 microns to maximize contrast. Two piston sensors, using a robust variation of dispersed fringes, determine piston shifts between the baselines and operate from 0.5 - 0.73 microns. All sensors are sampled at 800 Hz and processed with a DSP computer and fed back at 200 Hz (3 dB) to the active optics. A 4 Hz error signal is also fed back to the tracking platform. Optical performance will be maintained to better than λ/8 rms in closed-loop.
Hourly UV Index values at 45 sites in Canada and 52 in the USA were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dew point temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of the UV Index distribution over North America were estimated from the derived UV irradiance for the period 1979-1987 and then presented in the form of monthly maps. Brewer UV measurements at 11 Canadian and 20 US sites and erythemal UV estimates from TOMS data were used for validation. Direct comparisons with Brewer measurements at 7 Canadian sites for the period in the 1990s when both pyranometer and spectral UV data were available demonstrated agreement within 2-3 percent except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.
Seasonal variability of solar UV radiation in ocean waters is estimated on a global scale by combining satellite measurements of scene reflectivity (TOMS), column ozone (TOMS) and chlorophyll concentration (SeaWiFS) with radiative transfer calculations for an ocean-atmosphere system. The new features are an extension of underwater radiative transfer (scattering and absorption) into the UV, inclusion of polarization in the above water diffuse radiances, the proper treatment of Fresnel reflection, and first order atmospheric backscatter of water-leaving radiance to the oceans. Maps of downwelling diffuse irradiances (Ed) at ocean surface and at different depths in the ocean, diffuse attenuation coefficient (Kd), and ten percent penetration depth (Z10) of solar irradiation are computed for open ocean waters. Results on spectral irradiances at 310 nm in UV-B and at 380 nm in UV-A part of the spectrum are presented with particular emphasis on the role of aerosols, clouds, and ozone in the atmosphere and chlorophyll concentrations in the ocean.
Compared to the visible spectral region very little is known about aerosol absorption in UV. Without such information it is impossible to quantify a cause to the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report preliminary results of an aerosol closure experiment where a UV-shadow-band radiometer (UVMFRSR, USDA UVB Monitoring and Research Network) and well-calibrated sun-sky radiometer (CIMEL, NASA AERONET network) were run side-by-side for several months at NASA/GSFC site in Greenbelt, MD. The aerosol optical thickness, τ, was measured at 340nm and 380nm by the CIMEL direct-sun technique. These results compared well with independent MFRSR τ measurements at 368nm (using total minus diffuse irradiance technique). Such comparisons provide an independent check of both instrument’s radiometric and MFRSR’s angular calibration and allow precise tracking of the UV filter degradation by repeating the comparisons made at somewhat regular time intervals. The τ measurements were used as input to a radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD) to infer an effective imaginary part of the UV aerosol refractive index (k). This was done by fitting the MFRSR diffuse fraction measurements to the calculated values for each UV spectral channel. Inferred values of refractive index and PSD allow calculation of the single scattering albedo, ω, in the UV and comparisons with AERONET ω retrievals. The advantage of utilizing diffuse fraction measurements is that radiometric calibration is not needed for the MFRSR since the same detector measures both the total and diffuse flux. The additional advantage is that surface albedo is much smaller in the UV than in the visible spectral range and has much less effect on aerosol measurements.
Increased levels of biologically harmful Uv radiatonhave beenshown to affec aquatic ecosystems, marine photocynmetiry, and their imapct on carbon cycling. A quantiative assessment of UV effectw requires an estimate of the in-water raiationfield. An esitmate of underwater UV radiatonis porosed based on satellit meausrments fromthe TOMS and SeaWiFS and modesl fo radiatve transfer (RT). The Hydrolight code, modified toe xtnd it to the 290 - 400 nm wavleength range, is used for REt calucaitons in theocean. Solar direc tandidffuse radiances at the ocean surfce are calculated using a fulll RT code for clear-sky coditions, whicha re then modified for clouds and aerosols.Teh TOMS total column ozone and reflectivity productsa reinputs for RT calcuaitons in the atmosphere. An essential component of the in-water RT model is a model of seawater inherent optical properties (IOP). The IOP model is an extension of the Case-1 water model to the UV spectral region. Pure water absorption is interpolated between experimental datasets available in the literature. A new element of the IOP model is parameterization of particulate matter absorption in the UV based on recent in situ data. The SeaWiFS chlorophyll product is input for the IOP model. The in-water computational scheme is verified by comparing the calculated diffuse attenuation coefficient Kd, with one measured for a variety of seawater IOP. The calculated Kd is in a good agreement with the measured Kd. The relative RMS error for all of the cruise stations is about 20%. The error may be partially attributed to variability of solar illumination conditions not accounted for in calculations. The conclusion is that we are now able to model ocean UV irradiances and IOP properties with accuracies approaching those visible region, and in agreement with experimental in situ data.
Most comparisons of TOMS estimates of surface UV irradiation with measured values from ground-based instruments have indicated a bias of the TOMS estimates toward larger values. A portion of this bias results from absolute uncertainties in the ground-based instruments. The comparison reported here is based on ground-based data from four
sites in the UGA/EPA Brewer network. The raw data from the ground-based instruments has been corrected for (1) stray light rejection, (2) the cosine errors associated with the full sky diffuser, (3) the temperature dependence of the response of the instruments and (4) the temporal variation in the instrument response reducing the estimated errors of the absolute irradiance values of each spectral measurement to < ±7%. Comparisons of TOMS with the surface
measurements are performed both at spectrally resolved wavelengths at the time of overpass and for erythemally-weighted daily-integrated doses. These comparisons are made for all days and for clear-sky days only. The comparisons are carried out using both linear regressions of scatter plots of the two sets of data and for mean differences with respect to both TOMS and the Brewer measurements. It is found that spectrally resolved comparisons suffer from inconsistencies at some of the sites that are believed to result from wavelength uncertainties in the Brewer; they are
therefore of more limited use than wavelength integrated data. A comparison based on daily-integrated doses shows only a small positive TOMS bias (4%) for clear-sky days with a somewhat larger bias (8%) for data taken from all days.
One of the key components in understanding how global climate change effects the biological environment on Earth is determining how the amount of UV radiation reaching the surface has changed in response. In order to accurately quantify such changes, the role of tropospheric aerosols in both changing the amount of UV surface radiation and affecting the measurement of such radiation must be better understood. In this paper we will provide an overview on our current understanding of troposheric aerosols and their effect on UV radiation. We will also describe how such aerosols are taken into account when trying to measure the UV surface radiation, and we will show how the diurnal variability of tropospheric aerosols lead to large errors in determining UV surface radiation from space measurements. Finally, we will describe how measurement from future sensors launched into orbit other than those low to the Earth can reduce such errors.
The new Version 8 TOMS 360 nm reflectivity time series 1980 to 1992 and 1997 to 2001 have been combined to estimate changes that have occurred over a 21-year period. The observed changes are mostly related to changes in cloud cover and aerosols, since the Earthy appears dark (2 to 6% reflectivity) at 360 nm. The relative radiance calibration of the two TOMS (Nimbus-7, N7 and Earth-Probe, EP) has been adjusted using the measured minimum reflectivity over mid-latitude ocean and land locations (±50°). The result is that the previously published N7 minimum reflectivity decreased by 0.02 and now matches the better-calibrated Earth-Probe/TOMS. Most of the local trend features seen in the N7 time series (1980 to 1992) have been continued in the combined time series, but the overall zonal average and global trends have changed. The correlation of cloud cover with solar activity (measured by the 10.7 cm solar radiation) that was present during the Nimbus-7 period (1980 to 1992) is no longer evident for the period 1980 to 2001. The key results include a continuing decrease in cloud cover over Europe and North America and an increase in reflectivity near Antarctica.
We show comparisons between ground-based measurements of UV irradiance less 380 nm and satellite TOMS UV retrievals within the whole period of TOMS measurements (1979-2000) over Moscow. We analyze the scale of temporal averaging of ground-based UV data taken with 1 minute resolution which should be used while comparing with TOMS data measured once per day within a relatively large footprint area (50-100 km2). Another objective is to study interannual variability of UV irradiance obtained by ground-based UV measurements and TOMS UV retrievals for the whole period of observation (1979-2000) over Moscow area. The analysis of interannual variations in satellite UV retrievals and ground-based UV irradiance is given together with examination of different atmospheric parameters, which are available from ground and satellite observations. A special attention is given to the comparisons of UV radiation obtained from ground and satellite measurements in spring season when the maximum ozone loss is observed. This is done together with the analysis of interannual variations in snow characteristics (snow albedo, snow depth, etc) and in cloudiness. We revealed the uncertainties in TOMS UV retrievals at specified atmospheric conditions by using ancillary information. The comparisons between TOMS and ground-based UV radiation in cloudless atmosphere with different aerosol optical properties are of particular concern.
Comparison of measured UV irradiance with estimates from satellite observation is potentially effective for the validation of the data from the two sources. Data from 10 Canadian Brewer sites were compared in this study with noon UV irradiance estimated from TOMS measurements. In general, TOMS estimates can successfully reproduce long-term and major short-term UV variations, although there are some systematic differences between the measurements at the ground and satellite-retrieved UV irradiance. Up to 9% of the Brewer-TOMS difference can be attributed to the Brewer cosine response error. This error depends on the solar zenith angle and cloud conditions and is different from instrument to instrument. When the cosine response of the Brewer instrument is considered and applied, the Brewer data are still lower than TOMS-estimated UV irradiance at most of the sites by 10% on average. The bias for clear-sky condition is smaller, about 4%, than for overcast conditions (about 20% on average) with some wavelength dependence. The bias was close to 0 at one station (Saturna Island), possibly due to its much cleaner air.
We evaluate the effects of possible enhancements of the current (version 1) TOMS surface UV irradiance algorithm. The major enhancements include more detailed treatment of tropospheric aerosols, effects of diurnal variation of cloudiness and improved treatment of snow/ice. The emphasis is on the comparison between the results of the version 1 TOMS UV algorithm and each of the changes proposed. TOMS UV algorithm does not discriminate between nonabsorbing aerosols and clouds. Absorbing aerosols are corrected by using the TOMS aerosol index data. The treatment of aerosol attenuation might have been improved by using newly derived TOMS products: optical depths and the single-scattering albedo for dust, smoke, and sulfate aerosols. We evaluate different approaches for improved treatment of pixel average cloud attenuation, with and without snow/ice on the ground. In addition to treating clouds based only on the measurements at the local time of the TOMS observations, the results from other satellites and weather assimilation models can be used to estimate attenuation of the UV irradiance throughout the day. The improved (version 2) algorithm will be applied to reprocess the existing TOMS UV data record (since 1978) and to the future satellite sensors (e.g., Quik/TOMS, GOME, OMI on EOS/Aura and Triana/EPIC).
Satellite instruments currently provide global maps of surface UV irradiance by combining backscattered radiance data with radiative transfer models. The models are often limited by uncertainties in physical input parameters of the atmosphere and surface. Global mapping of the underwater UV irradiance creates further challenges for the models. The uncertainties in physical input parameters become more serious because of the presence of absorbing and scattering quantities affected by biological processes within the oceans. In this presentation we summarize the problems encountered in the assessment of the underwater UV irradiance from space-based measurements, and propose approaches to resolve the problems. We have developed a radiative transfer scheme for computation of the UV irradiance in the atmosphere-ocean system. The scheme makes use of input parameters derived from satellite instruments such as TOMS and SeaWiFS. The major problem in assessment of the surface UV irradiance is to accurately quantify the effects of clouds. Unlike the standard TOMS UV algorithm, we use the cloud fraction products available from SeaWiFS and MODIS to calculate instantaneous surface flux at the ocean surface. Daily UV doses can be calculated by assuming a model of constant daily cloudiness. Both SeaWiFS and MODIS provide some estimates of seawater optical properties in the visible.
Comparisons of UV irradiances measured by the USDA UVB Monitoring and Research Network at 305 and 368 nm with retrievals from the NASA TOMS and a multiple scattering radiative transfer code were made for an 18-month period from January 1, 2000 through May 31, 2001 for Las Cruces, New Mexico, USA (32.6 degree(s)N, 106.7 degree(s)W, 1317 m elevation) and Billings, Oklahoma, USA (36.6 degree(s)N, 97.5 degree(s)W, 317 m elevation). Agreement is generally within +/- 12% for all sky conditions and 8% for clear skies. The effects of aerosols is mostly less than 5%, consistent with the measured aerosol optical depths at 368 nm within the range of 0.05 and 0.25.
TOMS has been the main satellite instrument for measuring the global distribution of the total atmospheric column of ozone since the first one was launched in 1978. The fifth instrument's launch is planned for August 2000. A key scientific objective of the TOMS mission is to monitor the trend of total global ozone, which requires the ability to detect a 1% change in ozone over a decade. This, in turn, requires high calibration accuracy and long-term stability in the TOMS ratio measurements between the solar spectral irradiance and the Earth spectral radiance. The calibration process requires not only knowledge of the radiometric response of the instrument, but also of various instrument characteristics to convert the instrument output to the value of the physical observable being measured. This is due to the fact that the object sources in measurements may have different characteristics from those of the radiometric standards, e.g., intensity, polarization, and spectral distribution; the process of calibration requires a complete set of instrument characteristics, e.g., linearity, spectral bandwidth, and straylight response, to compensate for the difference between the standards and the source being measured. This paper describes methodologies of the TOMS FM-5 prelaunch tests that are relevant to calibration.
Meteor-3M(2)/TOMS-5 is a cooperative joint mission between the Russian Space Agency (RSA) and the United States (US) National Aeronautics and Space Administration (NASA). A US Total Ozone Mapping Spectrometer (TOMS) instrument is scheduled to be flown aboard a Russian Meteor-3M satellite in the year 2000. The main science objectives of the mission are to continue global total-ozone measurements to monitor long-term change in global total ozone, to understand processes related to the Antarctic ozone hole, and to improve the understanding of the processes that govern global total ozone. Secondary objectives are to measure aerosol amounts (dust, smoke, volcanic ash, and sulfates) and SO2. This paper describes the Meteor-3M(2) spacecraft, the TOMS-5 experiment, operations of Meteor- 3M(2)/TOMS-5, and plans for data processing, data archiving and distribution.
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