The OLI requirements specified a sensor that collects image data for nine spectral bands with a spatial resolution of 30 m (15 m panchromatic band) over a 185 km swath from the nominal 705 km LDCM spacecraft altitude. Key requirements include: a five-year design life; spectral band widths, center wavelengths, and cross-track spectral uniformity; radiometric performance including absolute calibration uncertainty, signal-to-noise ratios, polarization sensitivity, and stability; ground sample distances and edge response; image geometry and geolocation including spectral band co-registration; and the delivery of data processing algorithms.
The OLI is required to collect data for all of the ETM + shortwave bands to partially fulfill the data continuity mandate. Table 1 provides the specified spectral bandwidths in comparison to the ETM + spectral bands along with the required ground sample distances (GSDs). The widths of several OLI bands are refined to avoid atmospheric absorption features within ETM + bands. The biggest change occurs in OLI band 5 (0.845–0.885 μm) to exclude a water vapor absorption feature at 0.825 μm in the middle of the ETM + near infrared band (band 4; 0.775–0.900 μm). The OLI panchromatic band, band 8, is also narrower relative to the ETM + panchromatic band to create greater contrast between vegetated areas and surfaces without vegetation in panchromatic images. Additionally, two new bands are specified for the OLI; a blue band (band 1; 0.433–0.453 μm) principally for ocean color observations in coastal zones and a shortwave infrared band (band 9; 1.360–1.390 μm) that falls over a strong water vapor absorption feature and will allow the detection of cirrus clouds within OLI images (cirrus clouds will appear bright while most land surfaces will appear dark through cloud-free atmospheres containing water vapor). Note that the refined near-infrared band (band 5) and the new shortwave infrared band (band 9) both closely match spectral bands collected by the MODerate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites. Note also that the OLI band widths are required to remain within plus-or-minus 3% of the specified band widths across the field-of-view.
|OLI spectral bands||ETM + spectral bands|
|#||Band width (μm)||GSD (m)||#||Band width (μm)||GSD (m)|
NASA placed stringent radiometric performance requirements on the OLI. The OLI is required to produce data calibrated to an uncertainty of less than 5% in terms of absolute, at-aperture spectral radiance and to an uncertainty of less than 3% in terms of top-of-atmosphere spectral reflectance for each of the spectral bands in Table 1. These values are comparable to the uncertainties achieved by ETM + calibration. The OLI signal-to-noise ratio (SNR) specifications, however, were set higher than ETM + performance based on results from the ALI. Table 2 lists the OLI specifications next to ETM + performance (Markham et al., 2003) for ratios at specified levels of typical, Ltyp, and high, Lhigh, spectral radiance for each spectral band. Commensurate with the higher ratios, OLI will quantize data to 12 bits as compared to the eight-bit data produced by the TM and ETM + sensors.
|OLI band||Ltypical SNR||Lhigh SNR|
|ETM + performance||OLI requirements||ETM + performance||OLI requirements|
Excerpted from Remote Sensing of Environment 122, James R. Irons, John L. Dwyer, and Julia A. Barsi , The next Landsat satellite: The Landsat Data Continuity Mission, 11-21, Copyright 2012, doi:10.1016/j.rse.2011.08.026, with permission from Elsevier
Courtesy of the journal Remote Sensing of the Environment