Geography Reference
In-Depth Information
The latter, utilized the current Google earth engine database version 7.1.322
developed in October, 2013 and Landsat 8 2013 data captured with the
Thermal Infrared Sensor.
The SRTM high resolution DEM with 3 arc-seconds of 90-meter
resolution has been mosaiced into seamless (gapless) near-global coverage (up
to 60 degrees north and south) making it one of the DEM with the wider
coverage. The SRTM captured elevation in two spatial resolution- 30-meter
and 90-meter. Only 90-meter spatial resolution data is available globally while
30-meter spatial resolution (1 arc-second) data is available for US territorial
coverage alone. SRTM carries onboard its space shuttle specially modified
radar device that collected elevation data on the 11-day mission in February
2000. However, it is a mosaiced elevation data delivered in 1 x 1 degree tiles
and also in various raster formats acceptable by most GIS applica-tion. The
digital data is freely available for download from US Geological survey's
EROS data center's website.
SRTM dataset is usually delivered in a preprocessed form which involves
filling in the voids (especially in Version 4.1) with improved hole-filling
algorithm which make use of ancillary data sources. The mission uses a dual-
antennae, single-pass interferometric synthetic aperture radar (INSAR) and
operates at a wavelength of 5.6 cm (C-band). Landsat 8 (L8) became fully
operational in April 11, 2013 and the satellite images the whole earth every 16
days in an 8-day offset from Landsat 7. Two optical sensors are onboard the
earth observation instrument (L8)-the operational land imager (OLI) and the
Thermal Infrared Sensor (TIRS).
Unlike other versions of Landsat data such as the Landsat multi-spectral
scanner (MSS), Landsat thematic mapper (TM), Landsat enhanced thematic
mapper plus (ETM+) with 4 bands, 7 bands and 8 bands respectively, L8 data
is composed of 11 bands and it is acquired at 100-meter spatial resolution,
which is resampled to 30-meter pixels in delivered data with 16-bit high
quality pixel values of surface data, scaled to 55,000 grey levels. It captures an
approximate scene size of 170 km north to south by 183 km east-west. The
OLI sensor captures data in the visible, near infrared and shortwave infrared
wavelength areas, including panchromatic band. The TIRS captures earth data
in two long wavelength thermal infrared bands. The OLI has 12 meters
circular error, 90 percent confidence and the TIRS is characterized with 41
meters circular error, 90 percent confidence (USGS, 2013).
Google earth engine is a powerful platform which combines the strength
of Google search engine with satellite data, maps, terrain and 3D data to make
both local and global geographic information available for end users (Nkeki,
