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Investigation:

SH-01 (Birkett / Jasinski / Costa)

LBA Dataset ID:

SH01_Sat_Radar_Altimeter

Originator(s):

1. Birkett, Dr. Charon M.
2. Costa, Marcos Heil
      3. Jasinski, Michael F.

Point(s) of Contact:

Birkett, Dr. Charon M. (cmb@nemo.gsfc.nasa.gov)
Costa, Dr. Marcos Heil (mhcosta@ufv.br)

Dataset Abstract:

Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large wetlands, rivers, and associated floodplains. A clear advantage is the provision of data where traditional gauges are absent. As part of LBA, a complete altimetric analysis of the Amazon Basin was undertaken. Here, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first ~7.5 years of the mission. (Birkett, et.al. JGR 2002)

Beginning Date:

1992-09-01

Ending Date:

2000-02-28

Metadata Last Updated on:

2010-10-11

Data Status:

In Preparation for Archive

Access Constraints:

Public

Data Center URL:

http://daac.ornl.gov

Distribution Contact(s):

ORNL DAAC User Services (uso@daac.ornl.gov)

Access Instructions:

Public

Data Access:

IMPORTANT: The LBA-ECO Project website is no longer being supported. Links to external websites may be inactive. Final data products from the LBA project can be found at the ORNL DAAC. Please follow the fair use guidelines found in the dataset documentation when using or citing LBA data.
Datafile(s):

RALNET-LBA:  http://essic8.umd.edu/RALNET-LBA
Access data via ORNL DAAC ftp site: Radar Altimeter Network Data:  Search at ORNL DAAC
Radar Altimeter Network Data:  Search at ORNL DAAC
Access zip file via ORNL DAAC ftp site: Radar Altimeter Network Data:  Search at ORNL DAAC

Documentation/Other Supporting Documents:

Data Set User's Guide:  Search at ORNL DAAC

Citation Information - Other Details:

Birkett, C.M., L.A.K. Mertes, T.Dunne, M.H. Costa, and M.J. Jasinski. 2010. LBA-HMET SH-01 Remote Sensing of the Amazon: Application of Satellite Radar Altimetry. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.

Keywords - Theme:

Parameter Topic Term Source Sensor
STAGE HEIGHT HYDROSPHERE SURFACE WATER TOPEX/POSEIDON RADAR ALTIMETER

Uncontrolled Theme Keyword(s):  Altimetric radar, River stage, Topex/Poseidon

Keywords - Place (with associated coordinates):

Region
(click to view profile)
Site
(click to view profile)
North South East West
Amazon Basin Amazon Basin 5.00000 -18.00000 -35.00000 -80.00000

Related Publication(s):

Birkett, C. M., L. A. K. Mertes, T. Dunne, M. H. Costa, and M. J. Jasinski, Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry, J. Geophys. Res., 107(D20), 8059, doi:10.1029/2001JD000609, 2002.

Data Characteristics (Entity and Attribute Overview):

Data Characteristics:

This dataset consists 126 text files. For download convenience a zip file containing all 126 text files is also provided: SH01finaldata.zip. Each text file presents information about the intersection of the satellite path with a major river, floodplain or wetland region in Amazonia, where it was possible to retrieve stage information. A certain number of these satellite-derived time series can be compared to nearby ground station data.



The first three lines in the .txt file identify the profile, with latitude, longitude limits of the satellite track extent, and the mean reference height (MRH) across this extent to which all other satellite overpasses are compared.



The columns indicate the cycle, julian day (jday), time (in seconds), the date of the pass (dd mm yy), followed by a relative height with respect to the MRH, and the estimated rms error on the height.



Example data records from typical file: top.p013.s004.a.v1a.txt



reference profile = tg240013.amaz.txt

geographical range: latmin-longmin= -3.770 -71.503 latmax-longmax= -3.740 -71.492

Mean Reference Height = 97.308m 0.109s

cycle Jday time(s) date height(m) error(m)

5 12724 26021.496 2 11 92 -5.673 0.172

6 12734 18733.649 12 11 92 -6.087 0.055

10 12773 75979.192 21 12 92 -2.570 0.107

12 12793 61403.080 10 1 93 -1.451 0.080

13 12803 54114.769 20 1 93 -2.000 0.111

15 12823 39537.455 9 2 93 -1.931 0.074

Data Application and Derivation:

Although the primary objectives are ocean and ice studies, altimeters have had considerable success in the monitoring of inland water bodies. In particular, these results demonstrate how submonthly, seasonal, and interannual variations in height can be monitored.



Advantages

* Day/night and all weather operation.

* Generally unhindered by vegetation or canopy cover.

* All determined surface heights are with respect to one common reference frame.

* Satellites are placed in repeat orbits (up to 1km either side of a nominal ground track) enabling systematic monitoring of rivers, lakes, wetlands, inland seas and floodplains.

* Has the potential to contribute height information for any target beneath the satellite overpass, thus contributing information where traditional gauge (stage) data may be absent.

* Satellite altimetric instruments have been in continuous operation since 1991 and new missions are scheduled for the next decade. There is therefore the ability to monitor seasonal to interannual variations during the lifetime of these satellites.

* Techniques have been validated and results published in peer-reviewed journals.

Quality Assessment (Data Quality Attribute Accuracy Report):

Quality Assessment:

Limitations

* These instruments are primarily designed to operate over uniform surfaces such as oceans and ice-sheets. Highly undulating or complex topography may cause data loss or non-interpretation of data.

* Retrieved heights are an average of all topography within the instrument footprint. Such values are further averaged in the direction of the satellite motion, giving, for example, one final height value every 580m (TOPEX/POSEIDON) or 350m (ERS) along the ground track. Altimetric values therefore differ from traditional gauge measurements which offer spot heights at specific locations.

* The height accuracy is dominated by knowledge of the satellite orbit, the altimetric range (distance between antenna and target), the geophysical range corrections and the size and type of the target.

* Unlike imaging instruments, altimeters only retrieve heights along a narrow swath determined by the instrument\'s footprint size. The effective footprint diameter can vary depending on the nature of the target, and can potentially range from several hundred meters to many kilometers.

* Minimum target size is controlled by the instrument footprint size and the telemetry/data rates, and also on the surrounding topography and the target-tracking method used.

* The satellite orbit scenario and target size also determine the spatial and temporal coverage. Improved temporal coverage is gained at the expense of spatial coverage for a single satellite mission.

* Major wind events, heavy precipitation, tidal effects and the presence of ice will effect data quality and accuracy.

Process Description:

Data Acquisition Materials and Methods:

A satellite radar altimeter is not an imaging device, but continuously records average surface spot\' heights as it transverses over the Earth\'s surface. Operating at ~13.6GHz, each altimeter emits a series of microwave pulses towards the surface. By noting the two-way time delay between pulse emission and echo reception, the surface height can be deduced. Each returned height value is an average of all surface heights found within the footprint of the altimeter. The diameter of the footprint depends on the surface roughness, but can typically range between 200m (for open pools of water in calm conditions) to a few kilometers (open water with surface waves). Each satellite is placed in a specific repeat orbit, so after a certain number of days the same point (to within 1km), on the Earth\'s surface is revisited. In this way, time series of surface height changes can be constructed for a particular location along the satellite ground track during the lifetime of the mission.

References:

Birkett, C. M., L. A. K. Mertes, T. Dunne, M. H. Costa, and M. J. Jasinski, Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry, J. Geophys. Res., 107(D20), 8059, doi:10.1029/2001JD000609, 2002.

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