A new collection of Earth science data is now publicly available to advance global studies of how our planet's lands, oceans, atmosphere and life all interact to define our world's water cycle, carbon cycle and climate system. These data are courtesy of the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra satellite. Whereas good MODIS data have been available since November 2000, the newly released data set, called Collection 3, marks a significant step forward in data quality and consistency.
"MODIS achieved a steady-state level of operations in November (2000) and since that time we have continued to make every attempt to improve the algorithms," said Team Leader Vince Salomonson, of NASA's Goddard Space Flight Center in Greenbelt, Md. "In June, we decided to provide the Earth science community with a set of consistently processed data products based upon our best efforts at that time."
Like a highly advanced digital camera in space, MODIS has been measuring visible and infrared wavelengths from all over our world at multiple scales of time and space since February 2000. MODIS extends the measurement heritage begun by CZCS and AVHRR, and now provides exciting improvements in spectral detail, spatial resolution and accuracy over previous sensors.
Collection 3 currently includes three months of data products - March, April and May of 2001 - and is now being expanded to encompass a one-year span from November 2000 to November 2001. These advanced, scientifically useful products are an intermediate step between the earliest beta-quality products and formally validated global data sets. Yet even in this intermediate stage, the team finds its MODIS data are of superior quality and provide an excellent new data set for global change studies.
This interdisciplinary collection of Earth science data includes information on more than 40 meteorological, biological and hydrological characteristics of the Earth, including some of the first ever routine, global observations of key Earth science characteristics, such as aerosol concentration over land and enhanced estimates of the effective leaf area of Earth's vegetation. Measurements of ocean temperatures and chlorophyll concentrations reveal more detail and variability than previously seen, while MODIS' chlorophyll fluorescence product adds a whole new dimension to studies of the marine biosphere.
MODIS' data products are available at spatial resolutions ranging from 250 meters per pixel, to 1 kilometer, to 1 degree; and range over time from daily, to weekly and monthly global composites. Production of MODIS' data products is divided among the team's three discipline groups: Atmosphere, Land and Ocean. Atmosphere Group Leader Michael King is excited by what he sees in the MODIS data.
"We now have the ability to track and characterize aerosol optical properties over land and ocean, globally," he said. "And we have an unprecedented ability to separate small particles that result from human activities and biomass burning from coarse particles that result naturally, such as sea salts and desert dust."
According to King, MODIS allows scientists to measure the differences in cloud optical properties for both water and ice clouds. The sensor can characterize the optical thickness of clouds and quantify the size of the particles within them. Moreover, MODIS is the first space-based sensor with a 1.37-µm channel, which is particularly sensitive to high, thin cirrus clouds.
Complementing its measurements of the atmosphere, MODIS carries a suite of channels that are particularly well suited for studies of the Earth's land and ocean surfaces. The idea is to observe and measure the interactions of the atmosphere with lands, oceans and life on our world. Another copy of the MODIS instrument will fly aboard Aqua in spring 2002 with an afternoon equatorial crossing to capture the daily variability of the Earth system.
According to Land Group Leader Chris Justice, MODIS is the first space-based sensor that enables scientists to remove comprehensively the effects of the atmosphere for relatively unobstructed measurements of the surface. Thus, MODIS' measurements of surface reflectance and radiance are used to generate higher-order data products, such as spectral albedo, enhanced vegetation indices, leaf area index and the fraction of photosynthetically active radiation absorbed by plants, land use and land cover change, fires and burn scars, snow and ice cover and land surface temperature.
MODIS sets a new precedent in terms of radiometric data quality, integration of many different algorithms for producing a suite of data products, data validation and quality assurance and improved resolution. "MODIS is capable of showing land cover dynamics - on a global scale, every day, at up to 250 meter resolution - that were not possible before," Justice noted. "It is becoming apparent that MODIS 250-meter data can help advance land research that requires higher resolution and frequent measurements."
Among the new products generated from MODIS, the Enhanced Vegetation Index (EVI) product and the Spectral Albedo Product are noteworthy and unique to MODIS. The EVI offers an alternative to the Normalized Difference Vegetation Index (NDVI) measurements and appears to respond better to changes in vegetation as a function of changing climate, changing seasons, land use and differing plant structures.
According to Ocean Group Leader Wayne Esaias, MODIS' global 1-kilometer resolution sea surface temperature and ocean color (chlorophyll) products are an order of magnitude better than the same measurements made by precursor sensors.
"The details and patterns in MODIS' bio-optical and sea surface temperature distributions is astounding," Esaias stated. "For the first time, we can see correlations between the physics and biology of the ocean at spatial scales that just weren't available to us before. MODIS also offers improved approaches for chlorophyll measurements, color dissolved organic matter, coccolithophore calcite and ocean productivity."
Additionally, MODIS measures ocean parameters together with important atmospheric variables, like aerosols and clouds, to give scientists a much more complete understanding of the ocean-atmosphere climate interactions.
NASA's Terra satellite is the flagship of the Earth Observing System series of satellites, part of NASA's Earth Science Enterprise, a long-term research program dedicated to understanding how human-induced and natural changes affect our global environment.