Two Landsat images of the same area acquired in different seasons show different pixel values over an unchanged concrete surface. What preprocessing step would most directly address this inconsistency?
APan-sharpening to improve spatial resolution
BAtmospheric correction to remove seasonal differences in atmospheric scattering and absorption, converting to surface reflectance
CEdge enhancement to sharpen feature boundaries
DPrincipal component analysis to reduce data dimensionality
Atmospheric conditions (water vapor, aerosol loading) vary between seasons, adding different amounts of path radiance and absorption to each image. Atmospheric correction removes these atmospheric contributions, yielding surface reflectance values that should be consistent for unchanged surfaces across dates. Without this step, apparent changes may be atmospheric artifacts rather than real surface change.
Question 2 True / False
Geometric correction of satellite imagery only requires knowledge of the satellite orbit and sensor geometry.
TTrue
FFalse
Answer: False
While orbital parameters and sensor models provide the initial geometric model, terrain-induced distortions (relief displacement) require a DEM for orthorectification, and residual systematic errors often require ground control points (GCPs) -- identifiable features with known coordinates -- for refinement. Without DEM-based orthorectification, images of mountainous terrain can have positional errors of tens to hundreds of meters.
Question 3 Short Answer
Explain the difference between top-of-atmosphere (TOA) reflectance and surface reflectance, and why the distinction matters for quantitative remote sensing.
Think about your answer, then reveal below.
Model answer: TOA reflectance is computed from sensor-recorded radiance by accounting for solar illumination geometry and Earth-Sun distance, but it still includes atmospheric effects (scattering and absorption). Surface reflectance additionally removes the atmospheric contribution to isolate the signal from the ground. The distinction matters because surface reflectance is the physically meaningful quantity that describes the surface material, while TOA reflectance conflates surface and atmospheric signals. Vegetation indices, spectral matching, and multi-temporal comparisons require surface reflectance for valid results.
TOA reflectance removes sensor and solar geometry effects; surface reflectance additionally removes atmospheric effects. The latter is required for any analysis comparing pixels across space, time, or sensors.