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• Introduction

• Background History

• MODIS Research Area

INTRODUCTION

   Perhaps never before has it been so critical that mankind increase his knowledge of the world in which he lives, specifically, the Earth and its atmosphere. The elements of land, water, air, and life are interconnected. Environmental problems are of great concern to many. A great number of individuals, scientists, organizations, governments, and members of academia are working independently and collaboratively, utilizing state-of-the-art technology and equipment, in a massive effort, a "Mission to Planet Earth," to acquire a greater understanding of the planet so that proper and effective solutions to problems can be sought. As with any problem or conflict, having more accurate and detailed information allows one to surmise a more legitimate solution. Organized, tested, and validated data is the key.

   This is precisely what our group, the MODIS Land Surface Reflectance Science Computing Facility, led by Dr. E. F. Vermote, seeks. Dr. Vermote is affiliated with the University of Maryland and NASA's Goddard Space Flight Center Biospheric Sciences Branch, and is involved with the MODIS (MODerate-resolution Imaging Spectroradiometer) project. The objective is to provide "a comprehensive series of global observations of the Earth's land, oceans, and atmosphere in the visible and infrared regions of the spectrum in such a way as to view the entire surface of the Earth every two days." "MODIS is the primary tool on the Earth Observing System satellites for conducting global change research" (MODIS Web site: http://modis.gsfc.nasa.gov )

BACKGROUND   HISTORY

   In 1989, the U.S. Congress authorized the establishment of the U.S. Global Change Research Program in an effort to acquire the scientific understanding necessary to develop national and international policies concerning global environmental issues, particularly global climate change. In conjunction with the U.S. Global Change Research Program, NASA, in 1991, launched its project, "Mission to Planet Earth," confirming its commitment and dedication to the global-scale examination of the Earth. The program, now known as the Earth Science Enterprise, is a study of the interactions of the Earth's environmental components: air, water, land and life, with a focus upon increasing understanding of natural environmental changes, as well as human-induced changes, and to differentiate between the two. NASA's unique vantage point from space makes this research possible.

   Free-flying satellites, like NASA's Upper Research Satellite (UARS) and Space Shuttle missions, such as the Atmospheric Laboratory for Applications and Science (ATLAS), as well as airborne and ground-based studies comprised the first phase of NASA's research plan. Then, in 1998, with the beginning of the second phase, the first Earth Observing System (EOS) satellite was launched, one of a series of 17 satellites, supported by ground and data systems, utilized in the development of a 15-year environmental database. A primary focus will be placed upon climate change and ozone processes.   

   The Earth Observing System (EOS), managed by NASA's Goddard Space Flight Center (GSFC), Greenbelt, MD, is the centerpiece of the Earth Science Enterprise. The mission depends upon EOS Data Gateway, which distributes the data to the scientists, who analyze it and use it to build computer models of the environment. EOSDIS will archive, manage and distribute data to users worldwide. With these data, members of the U.S. Global Change Research Program, plan to develop and implement environmental policies that will benefit the Earth, and, thus, mankind, as well.

   NASA's Terra satellite will provide the first major part of the 15-year environmental dataset. On December 18th, 1999, Terra, carrying its five special sensors, one sensor being the MODIS instrument, was launched aboard an Atlas/Centaur 2-AS rocket from Vandenberg Air Force Base, California. This would be day one of the Terra mission, the MODIS mission, day 1999/001.

   Approximately two months later, February 24th, on the second descending orbit, the nadir aperture door was opened, and MODIS, with its delicate optics and electronics, commenced with its acquisition of data, data to be utilized in the creation of scientifically engineered images of the Earth and its atmosphere. These data would be used to create "early images," images that would allow scientist to analyze the consistency and the accuracy of the data, ensuring "Quality Assurance," and "Validation" of the data. The Terra instruments produce more than 850 gigabytes of data per day. For further reference in regards to the five Terra sensors, refer to

 http://terra.nasa.gov/About/ .
 

   The MODIS instrument is the sensor with which our group, the Land Surface Reflectance Science Computing Facility, is associated. MODIS is capable of viewing the entire globe daily at moderate resolutions, ranging from 250 meters square to 1 kilometer square (about 0.5 square miles) pixels. With a sweeping 2,330-km-wide viewing swath, MODIS sees every point of our world every 1-2 days in 36 discrete spectral bands. It tracks a wider array of the earth's vital signs than any other Terra sensor. The sensor measures the atmosphere, ocean, and land processes, and, thus, structurally and logically, the MODIS project is divided into three separate disciplines: atmosphere, ocean, and land, each a separate entity, yet interacting in conjunction. In a collaborative effort, two other groups, Quality Assurance and Validaion, act with the other groups to maintain data accuracy and consistency, thereby playing a vital role in the overall process. Still further, these groups are divided into more specialized disciplines, or projects.

    As members of the MODIS Land group, we are responsible for producing the MODIS Surface Reflectance product, also known as atmospheric correction. The MODIS Surface Reflectance product is a seven-band product computed from the MODIS Level 1B land bands 1, 2, 3, 4, 5, 6, and 7 (centered at 648 nm, 858 nm, 470 nm, 555 nm, 1240 nm, 1640 nm, and 2130 nm, respectively). The product is an estimate of the surface spectral reflectance for each band as it would have been measured at ground level as if there were no atmospheric scattering or absorption. It corrects for the effects of atmospheric gases, aerosol, and thin cirrus clouds. The atmospheric correction will be conducted for every pixel identified as being cloud free (using MOD03, cloud mask) and acquired for a solar zenith angle of less than 75 degrees. The Surface Reflectance product is a major input utilized in the generation of several land products: Vegetation Indices (VIs), BRDF (Bi-directional Reflectance Distribution Function), Snow cover, Thermal Anomaly, Leaf Area Index/Fraction of Photosynthetically Active Radiation (LAI/FPAR), and Land cover. Therefore, the MODIS Land Surface Reflectance product is an important and essential element, and will provide key information in the search for effective solutions for the Earth's environmental issues.

MODIS RESEARCH AREA

A global Land Surface Reflectance Product for use in the MODIS land algorithm

   The NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument will provide a global and improved source of information for the study of land surfaces with a spatial resolution of up to 250m. Prior to the derivation of various biophysical parameters based on the surface reflectances, the top of the atmosphere signals need to be radiometrically calibrated and corrected for atmospheric effects. The research focus is on establishing techniques that will be used for operational atmospheric correction of MODIS bands 1 through 7, centered at 648 nm , 858 nm, 470 nm, 555 nm, 1240 nm, 1640 nm, and 2130 nm, respectively.

   Previous operational correction schemes have assumed a standard atmosphere with zero or constant aerosol loading and a uniform Lambertian surface. The work focuses on the inversion of the MODIS measured signal into surface reflectance which is a necessary input to several higher level algorithms in the land processing chain and builds on research outlined in the existing ATBD (Algorithm Technical Background Document). Surface reflectance is a critical At-launch Standard product for MODIS. All land products (with the exception of surface temperature) require surface reflectance as an input.
 

Global distribution of aerosol optical thickness from MODIS/Terra.

Principal Investigator:

Dr. Eric F. Vermote
University of Maryland
Department of Geography
and NASA GSFC code 614.5

Correspondence to:

4321 Hartwick Rd.
Suite 209
College Park, USA
E-mail: mod09@ltdri.org