LTER Network Office Remote Sensing, GIS and Technological
Coordination Background
John Vande Castle, 2/96 - last edited 8/98
Introduction
The LTER Network Office (NET) installed Geographic Information System (GIS) technology
in support of Network level research at the same time that individual LTER sites were
funded through technological improvement supplements for electronic networking, Geographic
Information System, and remote sensing image processing technology. Support for the
LTER Network follows guidelines outlined in early technology development reports.
NET has integrated this activity within the framework of the LTERnet information system.
The goal of the work is to assist the research of the sites by facilitating technical
aspects of GIS/RS data and tools. The aim is to cover aspects of GIS/RS that is useful to
the LTER Network as a common group, more than aiding any individual site research program
- although this type of assistance is given when needed. This report is meant to be a
short example of information for reference and review. It is not a comprehensive list of
all ongoing activities at NET, but presents a few key examples of some of the Network
level service and research support provided by NET.
The focus for remote sensing and GIS activities at NET is for data acquisition and the
cross-site, large-scale collaborations which are afforded by these data. More important is
a focus for linking the technically oriented scientists specializing in these data with
other ecological researchers. GIS information at the national and global scale is highly
specialized and complex. Recognition of this requires a need to create ties with key
leaders of remote sensing and GIS activities in national, and more recently international
programs. Such links have been made to both commercial and government programs, in
particular to various programs within NASA, the USGS - in particular Oak Ridge National
Laboratories (Oak Ridge DAAC), the EROS Data Center, programs at NOAA, EOSAT (distributor
or Landsat data) and SPOT Image Inc. In addition, close contacts with lead software
vendors for tools used in remote sensing and GIS work, have been established in both the
commercial and public sector. NET has acquired beta versions of major software (Arc/INFO,
ERDAS, etc.) and has worked closely with the companies - providing feedback on the utility
of the software for large-scale ecological research. The variety and large amount of GIS
data in use by NET has made extensive use of the various software tools.
Communication and assistance with LTER site personnel has also been a key role of the work
at NET - assisting with data access (those archived here at NET, as well as where to
locate other data), data distribution, data archive, and access to software. This work is
integrated with the services of the LTERnet information system.
NASA Linkages
Early work with NASA has been a very fruitful collaborative research effort for
LTER Network as a whole, as well as individual site programs. More complete information
can be found on the "LTER/NASA page". Rather than being
just an exercise in data access, this work is a true collaboration, with NASA viewing the
LTER Network as an important link for their research programs with the LTER Network
benefiting from the expertise of NASA scientists. More important to the data access has
been linking various levels of expertise within the NASA programs with LTER science. An
example of this is within the sun photometer activity (described later) where the
technical and scientific expertise of NASA has provided a springboard for important
satellite data correction information, and in exchange, an important link by NASA to LTER
researchers on the ground. Individual site programs have acquired specialized aircraft and
satellite data ranging from digital high resolution AVIRIS to experimental MODIS simulator
data. Future work is planned to encourage collaboration of these more experimental
datasets. For the present, collaborations with more operational data sources such as
Landsat-TM and NOAA-AVHRR data are underway between NASA-EOS and LTER. All LTER sites were
included in work with the NASA global change program. In part of this work, NASA paid for,
and provided full Landsat-TM scenes for all of the LTER sites, with most sites receiving
multiple scenes during 1992 and1993. More recently additional dataset during 1993, and
1995 have been acquired with atmospheric correction of Landsat-TM data as part of a NASA
grant. Most sites are also included in the NASA Pathfinder programs, where historic and
present Landsat and AVHRR data are acquired for comparison with ground based measurements.
These activities with NASA are expected to continue and expand. Currently a proposal is
under review by NASA for extending research with the ongoing sun photometer activity, and
14 of the sites are working on a regional scale landscape characterization proposal to be
submitted to NASA within the next month.
Data Acquisition
Regular acquisition of data from the Thematic Mapper (TM) sensor system of the Landsat series of satellites was seen as an important source of unbiased, systematic, and comparable data for use by the LTER sites. This need was documented in past technology reports known within the LTER Program as the Shugart report and the Gosz report. Information regarding this and past recomedations for remote sensing and GIS for LTER sites can be found in the initial document for the "Minimum Standard Installation" know as the MSI. This need was explored further in an LTER funded workshop lead by John Aber resulting in the initial acquisition plans. Since these data are expensive, proprietary, and difficult to acquire, NET started an initial acquisition of these data for each site in 1991. The details of the acquisition were presented at meetings and published in proceedings volumes for reference (ERDAS users group - Atlanta, 1991; GIS/LIS, 1991). A special license was arranged to enable a single scene to be used by all LTER sites. This was a large change in EOSAT policy, and lead to further changes in data licenses by other groups (such as state-wide TM purchases by GAP researchers). The data acquired were screened for cloud cover (almost 50% of scenes deemed acceptable by EOSAT were returned for reacquisition), sent to the individual sites, and placed online via optical disk of the LTERnet information server (this has since been moved to an external mass storage system described later). The copy maintained at the network office has been an important source for intersite research as well as a known location of these data for the sites. NET receives regular requests for replacement copies of the data from individual LTER sites.
From a series of efforts by NET with NASA headquarters, a large number of full
Landsat-TM scenes (primarily 1992 and 1993) were acquired for all of the LTER sites, some
providing multi-temporal data which will be extremely important for future seasonal change
and cross-site comparative research. All of these data were distributed to the sites,
documented, and placed into near-line mass storage access.
High resolution SPOT-HRV data have been acquired for most sites in 1991 with similar
license arrangements as those for the EOSAT TM data. These data provide panchromatic 10m
resolution data - a substantial improvement over 30m TM data. Again these data were
distributed to the sites and placed online.
AVHRR (Advanced Very High Resolution Radiometer) data come in many forms since these
data are from a public domain, operational satellite program covering the earth more than
once/day. Most useful for LTER research are those data ingested and processed by USGS/EDC
in Sioux Falls, SD. A number of single pass satellite images have been acquired for
comparison with other data, but the operational processing of the raw data into 1km
vegetation index data (NDVI) has been relatively simple to acquire. Since 1990, these data
have been ordered on CDROM, sent to the sites, and preserved offline at NET. Ancillary
data comprise most of the CDROM information. The actual NDVI data are relatively small
(2-3gb total), and these data have been subset from all CDROMs and placed online. A few
AVHRR datasets have been acquired from NOAA (LUQ for instance is only contained in the
NOAA data acquisitions), and future plans may involve use of these data for sites outside
of the US continent.
Research Support
One large task at NET is to provide general information regarding remote sensing and
GIS research questions. This is primarily a consulting task, but is also a large part of
the on-going data acquisition, data access, and research work at the sites as well as here
at NET. In 1992, NET supported the sabbatical research of Dr. John Magnuson from NTL-LTER.
This research involved an extremely intensive research task to process and classify full
Landsat-TM scenes for regional comparison of the sites. The initial work generated over
6gb of processed data. Since his sabbatical, this collaboration has been maintained, and
much of the data reprocessed to take advantage of the tools in more recent software. For
instance, a serious limitation to this research was the need to convert all model output
to 8 bit data. The newer NDVI calculations (numbers ranging from -1.0 to +1.0) can be
easily stored unchanged as floating point numbers, eliminating a number of serious
processing limitations. All of the reprocessed data are kept in mass storage - an
additional 9gb of data.
GIS Data Archive
Most GIS data archived at NET are stored in the original format supplied by vendors or archive centers. The purpose of this is to maintain the original data format until a truely universal data format is accepted by researchers and GIS software vendors. Original data supplied in tape format (i.e. 6250BPI reels) have been read to disk and with a backup version on 8mm tape. All data are currently stored on-line in a 120gb RAID (level 5) linked to an MS-NT server and shared to the Unix servers by Integraph's "NFS Diskshare" utility. The RAID archive is also written to reduntant 24gp DDS3 tape for backup.
ERDAS/Imagine is used for processing and storing most raster-based information. This
hierarchical file (hfa) format not only permits easy access, but internally stores
important metadata information which can be easily exported, used for external metadata
generation, or used within the software itself for self-documentation of the data. For
instance, the most recent version of the software contains a data structure to store all
ancillary data information (i.e. tape header data) we used to process separately, and
maintains this information within the hfa structure An example is shown in Figure 1, where
a data catalog including metadata, was easily generated by the software for use in a
paper. In addition, specialized programs can be written by object programming within the
software, or by direct "C" code compilation for data and metadata access. The
important understanding of the long-term implications of this data storage is well noted
at NET. These formats will change over time, but the need for a common archive format now,
is required simply because it is not practical to attempt a data archive in the many
formats that are present for these data. This "active" archive is expected to
change with time, and if a common data format for storage of these data becomes a true
standard, these data will be translated. Staff expertise is involved in knowing if changes
in computer architecture or software requires a conversion effort of the data. However, to
date even with the heterogeneous hardware and software used at NET (Erdas/Imagine on Sun
Unix, Windows-NT and Windows-95), there has not been any problem or concern with the data
formats and storage conventions used. If needed, the original format can be recreated by
the software, and in fact is done on a regular basis. Recordable CDROM (CDR) is the
current media of choice for off-line distribution. CDR's are currently less expensive than
data quality 8mm tape (the past media of choice) and are less computer platform specific.
Arc/Info is used for vector data, but primarily is the source for data processed or
distributed in this form - for instance on CDROM. An example is the digital chart of the
world, acquired through a donation by ESRI, and stored by "tiles" (pieces of
Arc/Info data that can be pieced together).
Figure 1.
Example of metadata information from LTER image archive.
Documentation and WWW:
Documentation of the GIS data has been an on-going and time intensive effort due to the
large amount and variety of data archived. For example, the current data archive is in the
range of 80gb - most of it imported, viewed, and used in metadata generation. For the
remote sensing image archive, all raw documentation data, (generally tape header files)
have been stored with the imported scene data. This information has also been translated
to World Wide Web (WWW) "html" format. NET currently uses its WWW
(http://www.lternet.edu) for most documentation. All Landsat-TM and SPOT image have been
subset and stored as .gif files, to use as browse images for reference. The combination of
this information - image file, .gif browse image, raw header file, and translated html
documents comprise information for the metadata currently used to document the remote
sensing data archive. The complete documentation of the data is then consolidated using
WWW access on the LTERnet information server. Actual data access is restricted by access
permission on the LTERnet information server by conventional computer security
procuedures. Primarily this means that complete access to information is available
though anonymous ftp, gopher and WWW services. Actual data access to maintain
license restriction where they exist are controlled by access permission on the file
server and mass storage archive. All data are stored on the LTER server in the
directory/folder /archive, and stored within that folder by site acronym. The easest
way to access "/archive" is with tools like "ftp", WS_FTP", or
unix tools like "xftp. An example of this is shown in figure 2. Use of
the current archive has been extremely reliable, with no known data loss to date (1990 to
1998). The structure of the archive also permits us to easily move the data to other
storage locations in the future.
Figure 2. An example of "WS_FTP" access to the image "/archive" on LTERnet
Sun Photometer Activity
One of the more recent efforts related to satellite image data is a link to state of
the art solar calibration work with scientists at NASA-Goddard. An LTER/EOS workshop at
SEV-LTER (one of 5 recently coordinated by NET) identified data calibration as a major
limitation to future use of satellite data. Instruments known as sun photometers are able
to take measurements to estimate the exact amount of light energy present at the earth's
surface at any time. These automated instruments collect solar information every 15
minutes and transmit this information via satellite to NASA-Goddard for processing. The
processed data are mirrored (as well as the "demonstrat" processing software) on
the LTERnet system. The raw data are accessed by graphical interface (shown in figure 3).
These data are used to estimate particulate and water vapor constituents in the atmosphere
(the two primary sources of optical interference). This information is then used to
estimate the exact energy levels reaching the earth, which can then be converted to fit
the wavelength and bandwidth of the various satellite sensor systems. This final
"product" is shown in figure 4. Since the initial Sunphotometer work, NASA
has expaned this to a large "AERONET" program. The Sunphotometer project
also initiated a small "atmospheric correction" project to produce atmosphericly
corrected Landsat-TM data. These additional datasets are maintained on-line, and the
final modified TM data are available in the public domain.
Figure 3. GUI "Timeline" access to Sun Photometer site data
Figure 4. Modeled output of Sun Photometer for Landsat-TM data calibration/correction
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