Question 5 of 6

Question 5 (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

a) Five elements of image interpretation [10 marks]. Photointerpreters systematically read an image through a standard set of visual elements, normally applied in this order of increasing complexity: tone/colour — the relative brightness or hue a feature displays, driven by its reflectance/emittance, and the single most basic clue (e.g. water is dark, dry bare soil is light); texture — the frequency of tonal change within an area (smooth vs. rough), which distinguishes surfaces of similar tone but different physical roughness (e.g. smooth pasture vs. textured forest canopy); pattern — the spatial arrangement of features (e.g. a rectangular field pattern vs. a dendritic drainage pattern), which reveals process or land use; shape — the outline/form of a discrete object (e.g. the meandering plan-form of a river vs. the straight edge of a road); size — a feature's dimensions relative to other known-scale objects on the image, used to rule out or confirm identifications of similar-shaped features at different scales; shadow — both a hindrance (obscuring ground detail) and a clue (revealing an object's height/profile in silhouette, and enhancing subtle topography under low sun angle); and site/association — a feature's position relative to other, more easily identified features (e.g. a linear tonal break at the toe of a slope, next to a river, is far more likely to be an earthflow than the same signature on a flat upland).

b) Landsat 8 Thermal Infrared Sensor (TIRS) thermal bands [10 marks]. Landsat 8 carries two dedicated thermal-infrared bands (Band 10, ≈10.60–11.19 μm, and Band 11, ≈11.50–12.51 μm) at a native 100 m ground sample distance (resampled to 30 m to match the optical bands in delivered products). The two bands together enable a split-window technique: because atmospheric water vapour absorbs the two bands by slightly different amounts, comparing their brightness temperatures allows the atmospheric water-vapour contribution to be estimated and removed, yielding a more accurate land surface temperature (LST) than a single thermal band could achieve alone (Band 11 in practice suffers from a stray-light calibration issue and is often used qualitatively, with Band 10 alone or a corrected split-window algorithm carrying most quantitative LST work). Applications of the TIRS thermal bands include land-surface-temperature and evapotranspiration mapping for agricultural water management, urban heat-island characterization, detecting and monitoring thermal anomalies (active fires, volcanic vents, coal-seam fires), and locating groundwater discharge/thermal plumes in surface water bodies — all applications that rely on Landsat 8's TIRS to extend the visible/NIR/SWIR OLI instrument's land-cover mapping into a genuinely independent, energy-balance-based measurement.