Daily Vegetation Monitoring with the MODIS Reflectance Anisotropy Products

1
Daily Vegetation Monitoring with the MODIS
Reflectance Anisotropy Products Yanmin Shuai1,
Crystal L.B. Schaaf1, Zhuosen Wang1, Miguel O.
Román1, Alan H. Strahler1, Xiaoyang Zhang2,
Xiaowen Li3, Xiaoyuan Yang1, Yonghua Qu3,
Jeffrey Morisette4, Robert Wolfe4, and David
Roy5 1Center for Remote Sensing, Boston
University, MA. 2 NOAA/NESDIS, Earth Resources
Technology Inc, MD. 3Center for Remote Sensing
and GIS, Department of Geography of Beijing
Normal University, China. 4NASA Goddard Space
Flight Center, Greenbelt, MD 5Geographic
Information Science Center of Excellence, South
Dakota State University, SD.
The MODIS reflectance anisotropy and albedo
products have been providing Bidirectional
Reflectance Distribution Function (BRDF) models,
albedo measures, and nadir view-angle-corrected
surface reflectances (Nadir BRDF-Adjusted
Reflectance or NBAR) for nearly a decade now. The
products have been widely used to initialize and
evaluate surface radiation schemes and vegetation
dynamics in climate and biogeochemical models,
and also serve as key inputs to the MODIS
operational land cover and phenology products.
The operational algorithm currently uses
multi-date, high-quality, multi-spectral,
cloud-free, atmospherically corrected surface
reflectances from both Terra and Aqua to provide
global quantities at a 500m spatial resolution
every 8 days. However, the product was originally
envisioned as a daily product utilizing the
multi-day data to reconstruct the general surface
BRDF while emphasizing the individual daily
observations to capture fine temporal resolution
changes. Long term data archive constraints have
limited the operational global product to an
8-day retrieval cycle, but the regional
requirements of more than 100 MODIS direct
readout stations have driven the development and
implementation of a daily direct broadcast
algorithm and the ability to generate localized
daily reflectance anisotropy models,
view-angle-corrected NBAR, and albedo products to
monitor land surface vegetation phenology and
surface radiation.
A rolling 16-day strategy with an emphasis on the
most recent observation, is utilized and the
resultant BRDF, albedo, and NBAR values are then
used to generate radiation products and
vegetation indices to monitor the daily surface
vegetation phenology. The research agricultural
station at Yucheng on the north-east China plain
(see figures below) has been used as an
evaluation study location. According to an
assessment of spatial representativeness (Román
et al., 2009), tower (point) albedo measurements
are adequately representing the surrounding
landscapes extending to 500m pixel albedos.
Frequent field specification of the winter wheat
growing season, as well as continuous low tower
measures of surface albedo, were collected during
the 2005 winter wheat growing season. The daily
albedo and EVI data compare well with these field
measurements despite the obvious differences in
scale. A piecewise logistic model (Zhang et al.,
2003) was fit with the daily EVI data and the
rate of curvature was shown to capture the
primary transition dates quite successfully.
Table 1. The field-based phenological winter
wheat stages at the Yucheng site
References 1. Zhang, X., Friedl, M. A., Schaaf,
C. B., Strahler, A. H., Hodges, J.C.F., Gao, F.,
Reed, B.C., Huete, A. (2003). Monitoring
vegetation phenology using MODIS. Remote Sensing
of Environment, 84, 471-475. 2. Román, M. O.
(2009). Use of In-Situ and Airborne Data to
Assess Satellite-Based Estimates of Directional
Reflectance and Albedo. PhD. Dissertation thesis,
Department of Geography and Environment, Boston
University.
Data Source Yucheng Experiment Station (YCES),
Chinese Academy of Sciences (CAS)?