In contrast to our previous blog, this weekâ€™s is a celebration of the Earth Observing-1 (EO-1) satellite whose death will soon be upon us.
EO-1 was launched on the 21st November 2000 from Vandenberg Air Force Base, California. It has a polar sun-synchronous orbit at a height of 705 km, following the same orbital track as Landsat-7, but lagging one minute behind. It was put into this orbit to allow for a comparison with Landsat 7 images in addition to the evaluation of EO-1â€™s instruments.
It was the first in NASAâ€™s New Millennium Program Earth Observing series, which had the aim of developing and testing advanced technology and land imaging instruments, particularly related to spatial, spectral and temporal characteristics not previously available.
EO-1 carries three main instruments:
- Hyperion is an imaging spectrometer which collects data in 220 visible and infrared bands at 30 m spatial resolution with a 7.5 km x 100 km swath. Hyperion has offered a range of benefits to applications such as mining, geology, forestry, agriculture, and environmental management.
- Advanced Land Imaging (ALI) is a multispectral imager capturing 9 bands at 30 m resolution, plus a panchromatic band at 10 m, with a swath width of 37 km. It has the same seven spectral bands as Landsat 7, although it collects data via a different method. ALI uses a pushbroom technique where the sensor acts like a broom head and collects data along a strip as if a broom was being pushed along the ground. Whereas Landsat operates a whiskbroom approach which involves several linear detectors (i.e., broom heads) perpendicular (at a right angle) to the direction of data collection. These detectors are stationary in the sensor and a mirror underneath sweeps the pixels from left to right reflecting the energy from the Earth into the detectors to collect the data.
- Atmospheric Corrector (LAC) instrument allows the correction of imagery for atmospheric variability, primarily water vapour, by measuring the actual rate of atmospheric absorption, rather than using estimates.
The original EO-1 mission was only due to be in orbit only one year, but with a sixteen year lifetime it has surpassed all expectations. The extension of the one year mission was driven by the Earth observation user community who were very keen to continue with the data collection, and an agreement was reached with NASA to continue.
All the data collect by both Hyperion and ALI is freely available through the USGS Centre for Earth Resources Observation and Science (EROS). At Pixalytics weâ€™ve used Hyperion data for understanding the capabilities of hyperspectral data. The two images shown in the blog are a subset of a scene acquired over fields in South America, with image to the right is a pseudo-true colour composite stretched to show the in-field variability.
Whereas the image at the topÂ is the hyperspectral data classified using a statistical procedure, called Principle Components Analysis (PCA), which extracts patterns from within the dataset. The first three derived uncorrelated variables, termed principle components, are shown as a colour composite.
Sadly, satellites cannot go on forever, and EO-1 is in its final few weeks of life. It stopped accepting data acquisition requests on the 6th January 2017, and will stop providing data by the end of February.
It has been a great satellite, and will be sadly missed.