Each graph of the time-series represents the variation over time of the vegetation
index (EVI2) for a user? selected pixel on the virtual globe of
Google Maps.
The EVI2 (Jiang et al., 2008)
is based on MODIS images from the MOD13,
Q1 product (collection 5, 16 days composite, and spatial resolution of 250 m) available at
NASA.
The time-series in the blue graph are from the EVI2 values that were pre-filtered
using the view zenith angle band, the blue band (surface reflectance), and the date
of image acquisition. The time-series in the red graph are from the EVI2 values
that were further filtered using wavelet transformation.
The 0 flag values in the orange lines shows the gap regions in the
time-series. These regions correspond the linear interpolated data
which the distance to the nearest valid pixel is greater than 32 days. The
gaps regions are characterized by the presence of cloud-contaminated data or other noise type.
More details about the filtering method can be obtained in Freitas et al., 2011.
Precipitation data:
The cumulative monthly rainfall series (millimeters per month) were constructed based on product 3B43 V6 of
TRMM
(Tropical Rainfall Measuring Mission) available at
NASA's Goddard Earth Science (GES)
Data and Information Services Center (DISC) Distributed Active Archive Center (DAAC).
The same time-series can also be visualized at
TRMM Online Visualization and Analysis System.
The TRMM pixel has a minimum area of approximately 0.25 degrees (approximately 27.7 km2). The
graph of the cumulative monthly rainfall is the TRMM pixel that corresponds to the nearest
geographic coordinate of the pixel represented by yellow polygon around the marker.
Projection:
The MODIS images were reprojected to the sinusoidal projection (WGS84 datum) using the
MRT
(MODIS Reprojection Tools) software. The graphs of the time-series represent the closest MODIS pixel to the depicted red balloon in the virtual globe of
Google Maps.
The MODIS pixel is from an area that corresponds to at least 250x250 meters
(more details about the MODIS sensor can be found in
Wolfe et al., 1998;
Wolfe et al., 2002 and
Rudorff et al., 2007).
Issues related to spectral mixture, borders and its relationship to the scale in which the
pixel is visualized should be considered. Furthermore, there is no information with regard
to the positioning accuracy and the acquisition date of the images available in the virtual
globe of Google Maps.
However, the images available at the virtual globe of
Google Maps
are very helpful to contextualize and better understand the time-series.
Altimetry:
In addition to the time-series graphs a tool was built to assess the
elevation anisotropy around the selected pixel of the virtual globe of
Google Maps (red balloon).
This tool uses the elevation model information available in the
Google Maps API application programming interface
The anisotropy visualization is a simple polar plot of elevation around two sample circles,
allowing a rapid view of the topography around the selected pixel. This tool allows interactivity
and provides a range of distance between the center of the selected coordinate and the sampled circles.
The use of the MODIS data should follow the guidelines presented in the
MODIS website.
MODIS data are distributed by the Land Processes Distributed Active Archive Center (LP DAAC),
located at U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS)
Center (lpdaac.usgs.gov).
The goal of the present portal is to facilitate the public access to the free available
time-series of the MODIS and TRMM data for visualizing land use and land cover change.
Its use is allowed and encouraged for studies and scientific analyses, and public
policies, as long as the data source is mentioned. Publication of images or data used
from this portal should be referenced using the following citation:
Freitas, R. M.; Arai, E.; Adami, M.; Souza, A. F.; Sato, F. Y.; Shimabukuro,
Y. E.; Rosa, R. R.; Anderson, L. O.; Rudorff, B. F. T. Virtual laboratory of
remote sensing time series: visualization of MODIS EVI2 data set over South
America. Journal of Computational Interdisciplinary Sciences, v 2 (1):57-68. 2011. no prelo.
(http://epacis.org/jcis.php).
Whenever possible, please, send us by e-mail (laf@dsr.inpe.br) a copy or reference
of your work or oral presentation in which the data available at this portal were
used. The reference send to us will be posted in the portal allowing to disclose your
work and informing the way data of this portal are being used.
Terms of use:
Using our services you agree to the following terms:
to accept and follow the policies of using Google products
(Terms and Conditions),
as maps and markers are displayed on Google Maps;