IN51B-1149
A 35 Year Earth Science Data Record of Gridded IR Atmospheric Radiances
We present the generation of a 35 year Earth Science Data Record (ESDR) of gridded level 1B atmospheric radiances at a 250 km spatial resolution from sources of satellite data including the Vertical Temperature Profiler Radiometer (VTPR), High Resolution Infrared Sounder (HIRS2/3/4), and Atmospheric Infrared Sounder (AIRS). We use the MODIS long wave channels to validate the calibration of the AIRS and HIRS data. VTPR is an operational 8-spectral channel infrared sounding system with an IFOV around 55km at nadir that operated from 1972 to 1979. The HIRS/2 sensor is a 20 spectral channel instrument with an IFOV approx. 20km, that flew from 1979 to 2001 forming a 22 year record. HIRS/3, is an advanced HIRS sounder that flew on NOAA 15-17 from 1998 to the present. HIRS/4, essentially the same as HIRS/3 except for an IFOV of 10 km has flown on the ESA Met 0p A from 2006 to present. AIRS on Aqua satellite launched on May 2002 has 2374 spectral channels from 3.7 μm to 15 μm and is well calibrated as compared with MODIS channels on the same satellite. Based on the Aqua Senior Project Review of available flight fuel, power and orbital maneuvers, the assessed life span of the satellite Aqua is estimated to be 2013. No such gridded data products of just the observed IR radiances are available since the emphasis for these sensors was the inference of temperature profiles from the observations for use in weather analysis and prediction. We have developed a system, SOAR, that provides gridded radiance data for AIRS and MODIS radiances that can meet the precision and accuracy required for a Fundamental Data Record (FDR). We are exploiting the IBM Cell blade cluster (at UMBC) of 250 processors to geolocate and grid the entire data volume of AIRS and MODIS instruments employing a data intensive raycasting algorithm. The Observation Coverage (obscov) based geolocation significantly improves gridded accuracy by 1 Kelvin Brightness Temperature over most regions on Earth, when tested with the 12 micron AIRS window channel. In addition, "obscov" gridding has improved coverage, and eliminated the stipling artifacts and distortions of gridded regions at the poles. Our implementation of the "obscov" technique supports spatial response functions that can differ among sensors. We employ the SOAR system to produce gridded radiance data records from AIRS, HIRS, and VTPR at 250 km resolution from level 1B data products for the different satellite data sources available online using the ray casting algorithm. We show in this paper that this 35 year data record is of sufficient length, calibrated accuracy and continuity to meet the ESDR definition to observe and determine climate variability and change related to certain atmospheric processes.
IN51B-1150
An Overview on the Project to Develop Consistent Earth System Data Records for the Global Terrestrial Water Cycle
We aim to develop consistent, long-term Earth System Data Records (ESDRs) for the major components (storages and fluxes) of the terrestrial water cycle at a spatial resolution of 0.5 degrees (latitude-longitude) and for the period 1950 to near-present. The resulting ESDRs are intended to provide a consistent basis for estimating the mean state and variability of the land surface water cycle at the spatial scale of the major global river basins. The ESDRs to produce include a) surface meteorology (precipitation, air temperature, humidity and wind), b) surface downward radiation (solar and longwave) and c) derived and/or assimilated fluxes and storages such as surface soil moisture storage, total basin water storage, snow water equivalent, storage in large lakes, reservoirs, and wetlands, evapotranspiration, and surface runoff. We construct data records for all variables back to 1950, recognizing that the post-satellite data will be of higher quality than pre-satellite (a reasonable compromise given the need for long-term records to define interannual and interdecadal variability of key water cycle variables). A distinguishing feature will be inclusion of two variables that reflect the massive effects of anthropogenic manipulation of the terrestrial water cycle, specifically reservoir storage, and irrigation water use. The overall goal of the project is to develop long term, consistent ESDRs for terrestrial water cycle states and variables by updating and extending previously funded Pathfinder data set activities to the investigators, and by making available the data set to the scientific community and data users via a state-of-the-art internet web-portal. The ESDRs will utilize algorithms and methods that are well documented in the peer reviewed literature. The ESDRs will merge satellite-derived products with predictions of the same variables by LSMs driven by merged satellite and in situ forcing data sets (most notably precipitation), with the constraint that the merged products will close the surface water budget. The primary land surface forcing variable, precipitation, will be formed by merging model (reanalysis) and in situ data with satellite-based precipitation products such as TRMM, GPCP, and CMORPH. Derived products will include surface soil moisture (from TRMM, AMSR-E, SMMR, SSM/I passive microwave and ERS microwave scatterometers), snow extent (from MODIS and AVHRR), evapotranspiration (model- derived using ISCCP radiation forcings from geostationary and LEO satellites), and runoff (from LSM predictions and in-situ measurements).
IN51B-1151
Sea State Bias in Satellite Radar Altimetry - Revisited
Typically, sea state bias (SSB) is estimated from altimetrically measured sea surface height (SSH), waveheight (SWH), and wind speed (U), differenced from a time mean at the same geographic location. We investigate whether this commonly used approach may introduce a spurious value in the estimates of SSB. We use H not from any radar altimeter but from a simulation by the ECCO-2 high-resolution ocean general circulation (numerical) model. Therefore, our SSH should have zero SSB, except for random noise. We check this by using a parametric and nonparametric dependence on SWH and U, as measured by Jason-1 data during 2003-2004, and consecutive cycle differences. Our parametric estimates indicate that the factor multiplying the cross term on SWH and U is remarkably stable for any pair of cycles, and overall there is a spurious effect of the order of a fraction of a percent of SWH. The nonparametric estimates show that the SSB using consecutive cycle differences is closer to zero and much more stable than SSB calculated by subtracting a mean. Whether parametric or nonparametric are used, subtracting from a mean introduces spurious effects.
IN51B-1152
Integrated Multi-Mission Altimeter Data for Climate Research
The science value of satellite altimeter data has grown dramatically over time as enabling models and technologies have increased the value of data acquired on both current and earlier missions. With the prospect of an observational time series extending into several decades with Jason-1 and the Ocean Surface Topography Mission (OSTM), and later an operational series of altimeters, researchers are pushing the accuracy bounds in order to monitor global sea level rate at an accuracy of a few tenths of a mm/yr. These stringent accuracy requirements necessitate additional improvements to the present, future, and historical data sets. Our approach is to correct a number of consistency issues in the current and historical record, and in doing so further reduce the overall error budget of the altimeter observations, validate the accuracy of the resultant sea surface height measurement, and to provide a practical 'research ready' product to the community. Under the auspices of the NASA MEaSURE's (Making Earth System data records for Use in Research Environments) program sea surface height Climate Data Records (CDRs) are being enhanced by availing ourselves of the recent remarkable progress made in improving (a) the geoid, (b) orbit geo-location, (c) ocean tide models, (d) calibrations of radiometers needed to remove long period trends in the wet troposphere corrections, (e) sea state algorithms, and (f) in the International Terrestrial Reference Frame. The measurement of mean sea-level change from satellite altimetry requires an extreme stability of the altimeter measurement system since the signal being measured is at the level of a few mm/yr. This means that the orbit and reference frame within which the altimeter measurements are situated, and the associated altimeter corrections, must be stable and accurate enough to permit a robust MSL estimate. Foremost, orbit quality and consistency are critical to satellite altimeter measurement accuracy. The orbit defines the altimeter reference frame, and orbit error directly affects the altimeter measurement. Orbit error remains a major component in the error budget of all past and present altimeter missions. For example, inconsistencies in the ITRF used to produce the precision orbits at different times cause systematic inconsistencies to appear in the multi-mission timeframe between TOPEX and Jason-1. However, with recent improvements in the satellite force models, reference systems, and modeling strategies, the orbit can be significantly improved as has been shown for GFO and T/P. Dramatic improvements foreseen in gravity field models anticipated from the GRACE Mission are currently being realized, further offering a very significant reduction in orbit error, including those which are of special concern given they are geographically correlated, yet mission specific. In this presentation we provide a status report on our progress to provide a consistent precise orbit that will geodetically tie all missions, and our proposed strategies to develop an Earth Science Data Record for sea surface height.
IN51B-1153
Making Coastal Altimetry Happen: a Prototype Envisat Processor From the COASTALT Project
The COASTALT Project, funded by the European Space Agency (ESA), aims at defining, developing and
testing a prototype software processor to generate new Envisat radar altimeter products in the coastal zone.
Ultimately, the plans are for ESA to routinely generate and distribute these new Envisat coastal altimetry
products, also in preparation for exploitation of data from the future altimetry missions, CryoSat and Sentinel-
3. These missions will have inherently improved coastal zone capabilities by virtue of the adoption of a Delay-
Doppler instrument. Whilst paving the way to this overall objective, the COASTALT partners also aim to:
a) carry out an extensive study of the possible improvements in geophysical corrections in the coastal zone,
and identify the best correction strategies
b) revisit the whole approach to waveform retracking, by assessing the capabilities of geophysically-based
retrackers in the coastal ocean, testing novel retracking schemes and strategies, identifying the best
candidate strategy for immediate operational application and producing a fully usable prototype of that
retracker, while at the same time seeding the research into the next generation or retrackers for Sentinel-3
c) assess the performance of the new retracked products over three coastal regions with different
characteristics, where a host of in situ measurements are available for validation
d) provide full documentation on the new product in a way that is consistent with – and can be integrated
with – the Envisat User Handbook
e) contribute to capacity building, outreach and dissemination of coastal altimeter data to a wider user base.
In this paper we will illustrate the research and development that has gone into points a) and b), leading to
the design of the coastal altimetry processor. First we discuss the different possible approaches to deal with
the problem of geophysical corrections in the coastal zone, including the assessment of models of the wet
tropospheric correction, the use of GPS-meteo observations and Global Ionosphere maps from GPS
tomography, and the use of regional models for the inverted barometer correction and for high frequency
and tidal de-aliasing. Then we illustrate and discuss the various options for coastal waveform retracking, and
describe the current plans for the design of the coastal altimetry processor to be implemented within
COASTALT. Results of an in-depth analysis of Envisat waveforms in two coastal regions are guiding the
definition of the retracking algorithms, and the work on corrections has driven the design of the architecture
of the processor.
http://www.coastalt.eu
IN51B-1154
Gridded Climate Data Records: Bias Patterns, Error Variance, and Effective Resolution of Sea Surface Temperature Data Sets
Sea surface temperature (SST) is the most visible climate variable in the forum of climate change debate. In climate studies they are usually used in the form of gridded data sets which are analyzed statistically or serve as boundary conditions for atmospheric general circulation models. Therefore for SST climate data records (CDRs), as well as for CDRs of other climate variables for which sampling patterns, calibration data locations, and sensors' resolution and accuracy change dramatically in a few years timescale, issues of gridding methodology, bias correction, and optimal blending of data from different sensors are inseparable from the problem of maintaining CDR-quality stability and accuracy in multi-year and multi-decadal data sets. Intercomparison of major representative gridded SST products from Global High-Resolution Sea Surface Temperature Pilot Project (GHRSST-PP) will be presented, their biases and time-varying errors will be discussed and tracked to the error characteristics of their inputs (AVHRR, MODIS, ATSR, AMSR, and in situ data), to their analysis techniques, and to physical small-scale and short-term variability in the SST fields. Effective spatial and temporal resolution of these data sets will be characterized. Methods to evaluate best achievable error and stability characteristics of optimal SST analyses as a function of effective target resolution will be discussed.
IN51B-1155
Climate Data Records of Satellite-Derived Sea Surface Temperature
The retrieval of sea-surface temperatures (SSTs) from satellite radiometers is a singularly successful achievement in the field of satellite oceanography. Starting with the Advanced Very High Resolution Radiometers on the operational NOAA polar-orbiting series, and continuing through to the current sensors on MetOp and the research satellites Terra, Aqua and Envisat, a time series of consistent global SSTs spanning more than two decades is now available. The key to the accurate SST retrieval is not so much in the accurate on-board calibration of the radiance measurements, although that is a necessary prerequisite, but lies in the successful correction for the effects of the intervening atmosphere. The determination of the residual error characteristics of the SST retrievals is a vital aspect of establishing the utility of these fields in a wide range of applications including weather and ocean forecasting, and in climate research. The requirements of a 'Climate Data Record' (CDR) include well characterized error estimates and traceability to a National Standard, if feasible. This presentation will cover the generation of CDRs of SSTs using comparisons between the satellite retrievals and ship-based measurements of the skin SST derived from well-calibrated infrared radiometers and spectroradiometers, with calibration traceable to national SI temperature standards, within the recommended framework of the Committee on Earth Observation Satellites (CEOS).
IN51B-1156
The Ocean Colour MEASURES project
Satellite ocean color data products are rarely considered beyond a single product, the surface layer chlorophyll concentration. However over the last decade, a wide variety of satellite ocean color products, relevant to understanding ocean ecosystems and their biogeochemistry, have been derived from remotely sensed ocean water-leaving radiance spectra. These relatively new ocean color data products are transforming our understanding of ocean biological and biogeochemical processes. As part of NASA's MEASURES project, we are creating and distributing for evaluation purposes a variety of ocean color products which are candidates to become Earth Science Data Records (ESDR"s), some of them from the merging of multiple sensors. Examples of products are: ocean inherent optical properties, phytoplankton functional groups, phytoplankton growth rates and carbon-based productivity rates. Quality indices for the products will also be generated and distributed to document changes with previous versions of a product, comparisons of similar data products and comparisons with in situ data sets. Algorithm and data lineage will be monitored through the whole process so users will know exactly what they get. The final suite of products that will qualify as ESDR's will be determined through consultation with a small advisory board and with the data users.
IN51B-1157
Development of global ocean color climate data records
Ocean color, or the spectral distribution of visible light upwelling from beneath the ocean surface, carries information on the composition and concentration of biological constituents within the water column. This oceanic biomass plays a critical role in the global carbon cycle, accounting for approximately half of the net primary productivity on Earth. With the launch of the Coastal Zone Color Scanner in 1978, NASA demonstrated that quantitative ocean color measurements could be made from spaceborne sensors, given sufficient corrections for atmospheric effects and a rigorous calibration and validation program. The launch of the Sea-viewing Wide Field-of-view Sensor in 1997 represents the beginning of NASA's on-going efforts to develop and maintain a global ocean color data record. This talk will describe some of the challenges to producing ocean color measurements from spaceborne sensors with sufficient fidelity for climate change research. Efforts to develop and maintain the continuity of the time-series through multiple missions and varying instrument designs will be highlighted, including measurements from the Moderate Resolution Imaging Spectroradiometer currently flying on the Terra and Aqua platforms. In addition, several international satellite sensors with ocean color capability are now in orbit or preparing for launch, and collaborations with these international missions will be discussed. Finally, plans for continuation and enhancement of the time- series through future NASA ocean color missions and advanced measurements will be presented.
IN51B-1158
Earth Science and Climate Data Records at the National Oceanographic Data Center
The NOAA National Oceanographic Data Center (NODC) serves as the nation's archive and long-term stewardship facility for a wide range of ocean observations. For centuries, these observations came primarily from ships and other platforms in the water, and in recent decades satellite-based sensors have begun delivering critical data as well. NODC provides to the community Earth Science Data Records (ESDRs) from both in situ and space-based platforms, with a particular emphasis on Climate Data Records (CDRs) geared toward understanding long-term variability in the ocean. Two of NODC's major CDR efforts will be presented. The first of these is the World Ocean Database (WOD) project, which focuses on the collection, quality control, and provision of ocean parameters throughout the depth of the world ocean using in situ profile measurements. The second effort relies on satellite-based observations of sea surface temperature (SST) and includes the Pathfinder and Group for High Resolution SST (GHRSST) programs. Despite having emerged from what are traditionally considered very different parts of the oceanography community, both WOD and Pathfinder/GHRSST share a surprising degree of commonality in their approaches to generating and reprocessing products, obtaining community consensus on their approaches, and encouraging wide usage of the resulting CDRs. These efforts will be discussed and compared with a focus on application of the concepts not only across ocean disciplines but to the generation of other ESDRs as well.
IN51B-1159
NSIDC Contributions to Cryospheric Climate Data Records
We assess NSIDC holdings as they relate to the development of consistent, calibrated time series – Earth Science Data Records for the cryosphere. Gaps in the documentation of the major cryospheric elements are identified in the Integrated Global Observing Strategy- Partnership (IGOS-P) cryosphere theme report. Filling these gaps will be a focus of the planned World Meteorological Organization's Global Cryosphere Watch (GCW). Snow cover extent from 1966 is the longest satellite record, and this data product is available from NSIDC as the Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent Version 3. The main gap in snow cover data is the absence in freely accessible archives of station snow depths, especially for European countries.. There is no uniformly reliable data set of in situ snow water equivalent although since 1979 global products from passive microwave satellite data are available from NSIDC as the Global EASE-Grid Monthly Snow Water Equivalent Climatology Product . Corresponding data on global sea ice extent and concentration are also available from 1979 and most earlier operational chart products are accessible via the Global Digital Sea Ice Data Base at NSIDC. Snapshots of Arctic ice thickness exist from 1958 to present from submarine and moored upward-looking sonars, although not all of the Arctic Ocean is covered by these data. The World Glacier Inventory lists about 100,000 (two-thirds of all) glaciers but there are major gaps around Greenland and Antarctica, in the Himalayas and the United States. There are outlines (shapefiles and associated metadata) for over 65,000 glaciers in the NSIDC Global Land Ice Measurements from Space (GLIMS) data base and work is underway to complete these databases. However, there are globally only about 30 continuous mass balance records and larger glaciers are poorly represented. There are piecemeal records of lake and river ice in national archives but those available from NSIDC number 748 water bodies and they are not being updated. Data on the Thermal State of Permafrost are well organized but the network is sparse. There is also a growing network of Circumpolar Active Layer Monitoring (CALM) sites, but there is a need for more Southern Hemisphere ones. A major problem is the current absence of any overarching organizational framework for cryospheric observations - an issue the GCW will hopefully address
IN51B-1160
The Value of Cloud Top and Surface Temperature Observations from the 1966 Nimbus II High Resolution Infrared Radiometer Historical Data Record
NASA's Nimbus II High Resolution Infrared Radiometer measured radiance temperatures of cloud tops, sea and land surfaces while in a polar, sun-synchronous orbit from May through November 1966. The instrument operated in the 3.5-4.1 micron atmospheric window region. Most HRIR observations were collected at night to avoid reflected solar radiation contributing to the emission from blackbody surfaces. At least two forms of the original observations have been retained by NASA, one in the form of 70mm film strips and a second containing digitized data on magnetic tape. In 2007, we began efforts to recover the historical record from the original 7-track tapes. The results provided a basis for understanding the instrument data and metadata structures, assessing calibration and geolocation information, and the mission's geographic and temporal coverage. This paper will examine the completeness and utility of this Nimbus II HRIR data record for consideration in future Earth science research studies. We will highlight an approach for making decisions about future recovery efforts, adding value for long term archive and data access strategies. Principle recovery and access concepts are offered for guiding preservation of this and similar sets of observations brought to you by EOSDIS.
IN51B-1161
Creating Airborne ESDR Products for Global and Regional Model Assessment
Since the early 1980s NASA and partner agencies have conducted over 30 major tropospheric airborne field campaigns to investigate atmospheric composition over a wide range of geographical regions, from the remote marine boundary layer to polluted urban centers. Compared to satellite data, airborne data provides a longer historical perspective, a more extensive suite of observed species/parameters, and higher spatial resolution both horizontally and vertically. Consequently, airborne observations are of unique value to the modeling community's ability to predict future atmospheric composition and its impact on climate change and air quality issues. Nevertheless, there are significant challenges in using airborne data for model assessment and validation, including the lack of a standardized data format or centralized data source. Furthermore, measurement uncertainties are often missing or poorly defined. Since these airborne datasets were collected using different in-situ instruments/techniques and multiple aircraft platforms, it is also imperative to assess the level of consistency among these measurements. To overcome these difficulties, NASA's MEaSUREs program funded a project entitled 'Creating a Unified Airborne Database for Assessment and Validation of Global Models of Atmospheric Compositions.' The primary objective of this project is to develop airborne Earth Science Data Records (ESDRs) by creating a unified database, which will be suitable for use in global and regional model assessment and validation activities, especially those organized by the Atmospheric Chemistry and Climate (AC&C), the Aerosol Comparisons between Observations and Models (AeroCOM), and the Hemispheric Transport of Air Pollutants (HTAP) communities. The Tropospheric Airborne Measurement Evaluation Panel (TAbMEP), a group of measurement and modeling experts, was assembled to address the critical issues of historical measurement uncertainty and measurement consistency. The first TAbMEP meeting (convened late summer 2008) focused on the 2004 ICARTT (Intercontinental Consortium for Atmospheric Transport and Transformation) field campaign dataset. The panel also provided guidelines for algorithms which will be used to create ESDRs by unifying the publically available datasets from airborne missions sponsored by NASA, NOAA, NSF, and international partners. To be presented are highlights of the panel assessment as well as proposed algorithms to assess measurement uncertainties and to unify airborne data sets generated from multiple instruments and/or airborne platforms.
IN51B-1162
Towards Version 3 of EOS MLS Science Data Processing
The EOS Microwave Limb Sounder (MLS) is one of 4 instruments on the NASA Aura satellite launched 15 July 2004. It includes in its measurement suite simultaneous global measurement of vertical profiles of several atmospheric chemical constituents (O3, HCl, ClO, HOCl, BrO, OH, H2O, HO2, HNO3, N2O, CO, HCN, CH3CN, volcanic SO2), cloud ice, geopotential height, and temperature. The MLS Science Investigator-led Processing System (SIPS) produces calibrated radiances (Level 1B), and validated sets of the above profiles (Level 2). This paper presents developments in the EOS MLS data processing towards Version 3 to produce more data products, to increase resolution in some products, and to improve on Version 2 that is 'validated'.
IN51B-1163
Creating a Long Term Ozone Data Record
The TOMS team at Goddard Space Flight Center was one of the first groups to create a long term record of total column ozone. A merged ozone data record (MOD) was created by consistently combining total column ozone data from TOMS and SBUV instruments. We are now working to expand this product by adding data from additional instruments, including data from OMI and the recently launched GOME-2 instrument. Data from the NPOESS OMPS instrument will extend the data record after the launch of NPP. We are currently working to produce an ozone vertical distribution data set by merging profile data from various instruments, including SBUV(/2), UARS and Aura MLS, Sciamachy, GOME and GOME-2. In order to insure a uniform product, reprocessing of data with a consistent algorithm is sometime necessary. OMI data have been processed using the v8 SBUV/2 algorithm. The ultimate goal is an ozone Earth Science Data Record (ESDR) - a consistent, calibrated ozone time series that can used for trend analyses and other studies.
IN51B-1164
Consistent, Long-Term Aerosol Data Records From SeaWiFS Over Land and Ocean
Climate research has determined that natural and anthropogenic aerosols affect the radiative balance of the Earth directly through their interaction with incoming solar and outgoing terrestrial radiation and indirectly through their role as cloud condensation nuclei. However, quantifying the radiative forcing by aerosols has been hampered by the lack of a global, high resolution, continuous dataset, and thus has been plagued by high uncertainties. For instance, the transport of aerosols, particularly dust, from Asia and Africa to the western United States and Caribbean respectively has been recognized for many years, but the actual quantity and character of aerosols being transported from these source regions is still under investigation. These uncertainties have made it troublesome to adequately determine even just the sign of the climate forcing due to global aerosols. In this work, we apply the current Deep Blue aerosol algorithm to measurements from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), which was launched on August 1, 1997. Reasonable agreements have been achieved between Deep Blue retrievals of aerosol optical thickness and those directly from AERONET sun photometers over desert and semi-desert regions. New Deep Blue products will allow scientists to determine quantitatively the aerosol properties near sources using high spatial resolution measurements from SeaWiFS and MODIS-like instruments. Well-calibrated, long-term satellite data records (1998 - present) from SeaWiFS will be utilized to investigate the interannual variability of source, pathway, and dust loading associated with the Saharan and Asian dust storm outbreaks. In addition, monthly averaged aerosol optical thickness from SeaWiFS will also be compared with the MODIS Deep Blue and other existing satellite aerosol products.
IN51B-1165
Web-enabled Landsat Data (WELD): a Consistent Seamless Near Real Time MODIS-Landsat Data Fusion for the Terrestrial User Community
IN51B-1166
Earth System Data Record Of Vegetation Leaf Area Index From Multiple Satellite-Borne Sensors: Evaluation And Validation
The evaluation of a new global monthly leaf area index (LAI) data set for the period July 1981 to December 2006 derived from AVHRR Normalized Difference Vegetation Index (NDVI) data is described. The theoretical principle in retrieving LAI from NDVI is based on a physical algorithm rooted on the radiative transfer theory of canopy spectral invariants. Establishing the consistency and validity of the long-term coarse resolution LAI product is a challenging task. Here, the implementation, production and evaluation of the data set are described. The data set is evaluated both by direct comparisons to ground data and indirectly through inter- comparisons with similar data sets. The indirect validation showed satisfactory agreement with existing LAI products, importantly MODIS, at a range of spatial scales, and significant correlations with key climate variables in areas where temperature and precipitation limit plant growth. The data set successfully reproduced well-documented spatio-temporal trends and inter-annual variations in vegetation activity in the northern latitudes and semi-arid tropics. Comparison with plot scale field measurements over homogeneous vegetation patches indicated a 7% underestimation when all major vegetation types are taken into account. The error in mean values obtained from distributions of AVHRR LAI and high-resolution field LAI maps for different biomes is within 0.5 LAI for six out of the ten selected sites. These validation exercises though limited by the amount of field data, and thus less than comprehensive, indicated satisfactory agreement between the LAI product and field measurements. Overall, the intercomparison with short-term LAI data sets, evaluation of long term trends with known variations in climate variables, and validation with field measurements together build confidence in the utility of this new 26 year LAI record for long-term vegetation monitoring and modeling studies.
IN51B-1167
Combining Data Sets to Generate the Optimum Global Digital Elevation Model
In 2000 the Shuttle Radar Topography Mission (SRTM) used radar interferometry to map the Earth's topography inside 60 degrees latitude, representing 80 percent of the land surface. The resulting digital elevation models bettered existing topographic data sets (including restricted military data) in accuracy, areal coverage and uniformity by several orders of magnitude, and have found very broad application in most of the geosciences, military operations, even Google Earth. Despite their popularity the SRTM data have several limitations, including lack of coverage in polar regions and occasional small voids, or areas of no data, in regions of high slope of low radar backscatter.. Fortunately additional data sets are becoming available that, although lacking SRTM's coverage and at times quality, are sufficient to mitigate many of these limitations. This includes SPOT stereo, ICESat laser profiles, airborne radar interferometry data, and most notably the soon to be released global DEM produced from ASTER stereo pairs. The MEaSUREs program is sponsoring an effort to merge these sets to produce and distribute an improved collection of data records that will optimize the topographic data, as well as make available additional data from the SRTM mission. There are four main areas of effort: 1. A systematic program to combine SRTM elevation data with those from other sensors, principally ASTER, to fill voids in the DEMs according to a prioritized plan, as well as extend the coverage beyond the current 60 degree latitude limit. 2. Work with the ICESat project team to combine laser altimeter topographic profiles with SRTM DEMs to produce and distribute data with enhanced ground control. 3. Document the existing SRTM radar image and ancillary data cells, as well as generate image mosaics at multiple scales and distribute them via the world wide web. 4. Generate, document and distribute a standard and representative set of SRTM raw radar echo data, along with the appropriate ancillary tracking and pointing data necessary to process the echoes into DEMS using improved algorithms or techniques.