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. 2017 May;9(5):412.
doi: 10.3390/rs9050412. Epub 2017 Apr 27.

EO-1 Data Quality and Sensor Stability With Changing Orbital Precession at the End of a 16 Year Mission

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Free PMC article

EO-1 Data Quality and Sensor Stability With Changing Orbital Precession at the End of a 16 Year Mission

Shannon Franks et al. Remote Sens (Basel). .
Free PMC article

Abstract

The Earth Observing One (EO-1) satellite has completed 16 years of Earth observations in early 2017. What started as a technology mission to test various new advancements turned into a science and application mission that extended many years beyond the satellite's planned life expectancy. EO-1's primary instruments are spectral imagers: Hyperion, the only civilian full spectrum spectrometer (430-2400 nm) in orbit; and the Advanced Land Imager (ALI), the prototype for Landsat-8's pushbroom imaging technology. Both Hyperion and ALI instruments have continued to perform well, but in February 2011 the satellite ran out of the fuel necessary to maintain orbit, which initiated a change in precession rate that led to increasingly earlier equatorial crossing times during its last five years. The change from EO-1's original orbit, when it was formation flying with Landsat-7 at a 10:01am equatorial overpass time, to earlier overpass times results in image acquisitions with increasing solar zenith angles (SZAs). In this study, we take several approaches to characterize data quality as SZAs increased. Our results show that for both EO-1 sensors, atmospherically corrected reflectance products are within 5 to 10% of mean pre-drift products. No marked trend in decreasing quality in ALI or Hyperion is apparent through 2016, and these data remain a high quality resource through the end of the mission.

Keywords: ALI; Advanced Land Imager; EO-1; Hyperion; Landsat-7; Precession; Solar Zenith Angle; data quality.

Conflict of interest statement

Conflicts of Interest: The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
EO-1 changes in precession rate started in 2011. Acquisition time at the Railroad Valley Playa declined from 10:12 to 8:14, reaching 8 AM in October, 2016. The stability of the overpass time from 2001 to 2008 is shown (within dotted box), for nadir views (open circles) as well as off-nadir views (filled circles). A 15 minute change in overpass time is indicated within ellipse, after EO-1 left the Landsat-7 formation. The decline of overpass time is indicated by the downward arrow, after onboard fuel was expended.
Figure 2
Figure 2
Solar zenith angles (SZAs), measured in degrees, of daytime Hyperion images. Due to the earlier acquisition times for the imagery, the distribution of SZAs at overpass times during 2015 shifted to larger values (red bars) than during the earlier normal mission operations (blue bars).
Figure 3
Figure 3
Solar Zenith Angles (SZAs) at EO-1 overpass time showing the effect of changing seasons and latitudes on SZAs as overpass time drifts to earlier times (colored lines, the colors indicating the latitude of the observation as shown in the legend). The blue shaded region shows SZAs at various latitudes during nominal operations, compared to SZAs experienced in 2016 (orange shaded region).
Figure 4
Figure 4
Mean reflectance and standard deviation for select wavelengths for the Rail Road Valley Playa (RRVP) site before late mission precession changes (2001–2008 data, n=15 images, ~10:05 am mean local time acquisition).
Figure 5
Figure 5
Statistics for median NDVI difference between Landsat and ALI sensors, per six National Land Cover Database (NLCD) classes. Red line is median, blue box is quartiles, and black crosses are outliers. NDVI values were derived from Top of Atmosphere (TOA) reflectance.
Figure 6
Figure 6
Upper chart: NDVI maps from EO-1 Hyperion images over the Howland Forest area in Maine across four seasons from: a) Spring; b) Summer; c) Fall; d) Winter. Three flux tower sites are indicated with black squares. Lower graph: NDVI difference between Hyperion and MODIS for the three flux tower sites in the Howland forest area of Maine from 2003 to 2014.
Figure 7
Figure 7
Spectrum (top row) and 1st, 2nd, 3rd derivatives (rows 2 to 4) of a Corn field (column A) and Evergreen patch (column B).
Figure 8
Figure 8
Spectrum (top row) and 1st, 2nd, 3rd derivatives (rows 2 to 4) of a deciduous patch (column C) and Rooftop (column D).
Figure 9
Figure 9
Change in reflectance anomaly (Δp) at select wavelengths. A mean was established by averaging values from 2001–2008. The dashed line above the bars shows the time of acquisitions and the key for wavelengths is presented in the lower right legend.
Figure 10
Figure 10
Means of 172 calibrated Hyperion bands from 36 images acquired from 2004 to 2016 after use of 3 atmospheric correction models: (top row) least squares fit linear trend in surface reflectance; (bottom row) coefficient of variation (CV). The quadrature (combined uncertainty) is calculated as the square root of the sum of squares. Gray areas indicate atmospheric absorption bands [52].

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