Question 1

Remote sensing and platform-induced errors: which of the following error sources can arise from the characteristics and motion of the sensor platform?

Accepted Answer

Introduction / Context: In remote sensing, the platform (satellite or aircraft) affects geometry, scale, and radiometry. Variations in altitude, attitude, and orbit parameters lead to distortions and registration errors that must be modeled or corrected in preprocessing. Given Data / Assumptions: Platform may be spaceborne (satellite) or airborne. Sensor collects imagery or other data over time. We focus on platform-induced geometric effects. Concept / Approach: Altitude (mean flying height) governs scale; altitude variation causes scale changes within/across scenes. Orbit drift alters ground track and local time of observation, affecting view geometry and illumination. Together, these induce planimetric distortions and misregistration if uncorrected. Step-by-Step Solution: Recognize altitude as a first-order control on image scale (larger height → smaller scale).Identify altitude variation as a source of non-uniform scale and relief displacement differences.Acknowledge orbit drift as a change in ground track/revisit geometry, affecting geolocation and temporal consistency.Conclude that all listed factors are valid platform-related error sources. Verification / Alternative check: Photogrammetry and remote sensing texts list platform altitude/attitude and orbit control as primary contributors to geometric error budgets. Why Other Options Are Wrong: Picking any single factor omits other genuine platform-induced errors. Common Pitfalls: Confusing sensor-internal distortions (lens, timing) with platform-induced geometric effects. Final Answer: All of these

Question 2

In remote sensing and atmospheric physics, the spectral region of electromagnetic radiation that passes through the Earth’s atmosphere with minimal attenuation is known as:

Accepted Answer

Introduction / Context: In satellite remote sensing and earth observation, not all wavelengths of electromagnetic radiation reach the surface or a sensor in orbit. Certain wavelength bands are absorbed by atmospheric gases such as water vapor, carbon dioxide, and ozone, while other bands pass through with comparatively little loss. These transmissive parts of the spectrum enable most optical, infrared, and microwave sensing systems to operate effectively. Given Data / Assumptions: The question asks for the term used to describe spectral regions with high atmospheric transmission. We consider radiation passing through the atmosphere with minimal attenuation due to absorption or scattering. Standard terminology from remote sensing is assumed. Concept / Approach: An atmospheric window is a spectral interval where the atmosphere is relatively transparent, allowing radiation to pass with limited attenuation. Common windows include parts of the visible and near-infrared (roughly 0.4–0.9 micrometres), shortwave infrared windows, the thermal infrared window near 8–14 micrometres, and specific microwave windows. These windows are exploited by passive and active sensors to maximize signal-to-noise and reduce atmospheric corrections. Step-by-Step Solution: Identify the phenomenon: minimal attenuation across specific wavelength ranges.Recall the technical term: 'atmospheric window' for transmissive bands.Eliminate distractors that are unrelated to transmission (e.g., 'ozone hole', 'black hole').Select the correct term: 'Atmospheric window'. Verification / Alternative check: Review typical sensor band placements (e.g., Landsat, Sentinel, MODIS) which align bands within known windows to reduce absorption by water vapor and CO2. Why Other Options Are Wrong: Ozone hole: a depletion region in the stratospheric ozone layer, not a spectral window. Ozone window: not a standard term in this context. Black hole: an astrophysical object; irrelevant to atmospheric transmission. Transmission gap: vague and not the established term. Common Pitfalls: Confusing physical atmospheric features (e.g., ozone hole) with spectral transmission concepts; assuming all visible light is fully transmissive without considering aerosols and Rayleigh scattering. Final Answer: Atmospheric window

Question 3

For a scanner viewing off-nadir by an angle θ (theta), the ground distance swept by the sensor's instantaneous field of view (IFOV) is proportional to which trigonometric function of θ?

Accepted Answer

Introduction / Context: In imaging geometry for whiskbroom and pushbroom sensors, the footprint of an instantaneous field of view (IFOV) projects onto the ground plane. As the scan angle moves away from nadir, geometric foreshortening and projection effects change both the linear dimensions and area of the ground resolution element. Understanding these relationships is crucial for interpreting pixel sizes, radiometry, and map scale across the swath. Given Data / Assumptions: θ is the scan angle measured from the nadir (vertical). The ground is a flat horizontal plane at mean terrain elevation. Small-angle IFOV in sensor space projects onto the ground by perspective geometry. Concept / Approach: For a given angular IFOV, the linear ground dimension along the scan direction increases approximately in proportion to sec θ, because the slant range and projection stretch grow with off-nadir angle. Consequently, the area of the projected IFOV scales roughly with sec^2 θ (one factor from the scan-direction stretch and another from the along-track or range-direction projection, depending on geometry and platform motion). Many remote sensing MCQs refer to the distance 'swept' in the sense of the effective ground extent covered per IFOV across the swath, which aligns with the sec^2 θ dependence for area-like coverage. Step-by-Step Solution: Relate ground-projected IFOV to off-nadir angle: linear scale ∝ sec θ.Recognize that total swept ground extent across and along the scan grows with two orthogonal stretches.Conclude that the proportionality for the swept extent (interpreted as composite coverage) is sec^2 θ.Select option: 'sec2θ'. Verification / Alternative check: Sensor geometry texts show pixel area increasing more rapidly off-nadir than a single linear factor, consistent with the sec^2 θ rule-of-thumb (ignoring Earth curvature and terrain). Why Other Options Are Wrong: sin2θ, cos2θ, tan2θ, cot2θ do not match the projection scaling for off-nadir viewing of a small angular IFOV. Common Pitfalls: Confusing linear dimension scaling (sec θ) with area scaling (sec^2 θ); ignoring that pixel sizes vary across-track in pushbroom imagery. Final Answer: sec2θ

Question 4

Electromagnetic wave polarization and incidence: which of the following statements about electric vector orientation, polarization naming, and the plane of incidence are correct?

Accepted Answer

Introduction / Context: Remote sensing systems (radar and optics) are sensitive to polarization. The naming conventions for polarization depend on the orientation of the electric field (E-field) relative to the plane of incidence, which is established by the incoming ray and the surface normal at the point of interaction. Correct comprehension of these conventions is important for understanding reflectance, emissivity, and radar backscatter behavior. Given Data / Assumptions: A plane wave impinges on a planar surface. The electric field defines the polarization state (linear polarization cases). Standard geophysical naming: vertical (p) and horizontal (s) relative to the plane of incidence. Concept / Approach: Linear polarization is defined by a fixed direction of the E-field vector. If the E-field lies in the plane of incidence (p-polarization), it is often called vertical polarization in geophysical literature; if the E-field is perpendicular to that plane (s-polarization), it is often called horizontal polarization. The plane of incidence is, by definition, the plane through the incident ray and the surface normal. These conventions underpin Fresnel reflection coefficients and explain different reflectivities for s and p polarizations. Step-by-Step Solution: Recall the definition of linear (plane) polarization.Relate p-polarization (E in plane of incidence) to vertical; s-polarization (E ⟂ plane) to horizontal.State the definition of the plane of incidence.All listed statements align with the standard conventions. Verification / Alternative check: Fresnel equations are commonly presented with s and p polarizations; experimental reflectance curves differ for each, confirming the practical importance of the definitions. Why Other Options Are Wrong: Each individual statement is correct; omitting any would give an incomplete picture. Hence the combined option is appropriate. Common Pitfalls: Mixing up vertical/horizontal labels between different conventions; forgetting that the naming is relative to the plane of incidence, not the ground. Final Answer: All of these

Question 5

The full electromagnetic spectrum spans an enormous range of wavelengths. Which of the following best represents the approximate overall wavelength limits (in metres) commonly cited in remote sensing and physics?

Accepted Answer

Introduction / Context: The electromagnetic (EM) spectrum encompasses gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. Remote sensing exploits specific sub-bands that are transmissive through the atmosphere and carry meaningful surface information. Knowing the rough overall limits of the spectrum builds intuition for sensor design and signal behavior. Given Data / Assumptions: The question seeks a broad, order-of-magnitude range of EM wavelengths. Exact boundaries vary by convention; approximate orders suffice. Remote sensing typically uses visible to microwave bands but understanding the full range is useful. Concept / Approach: Common physics references cite the spectrum over many decades of wavelength. A representative overall span goes from about 10^-10 m (hard X-ray/near gamma region) to around 10^10 m (long radio waves). While the exact endpoints can differ slightly, this selection captures the intended magnitude across 20 orders. Step-by-Step Solution: Compare each option's lower and upper exponents to typical references.Note that 10^-10 to 10^10 m covers gamma/X-ray to very long radio wavelengths.Select that range as the best overall descriptor. Verification / Alternative check: Physics texts and EM spectrum charts show practical ranges extending even further in some conventions, but 10^-10 to 10^10 m is a commonly accepted broad span. Why Other Options Are Wrong: 10^-8 to 10^6 m and 10^-8 to 10^8 m under-represent the extremes. 10^-10 to 10^6 m cuts off very long radio wavelengths. 10^-12 to 10^2 m is too narrow at the radio end. Common Pitfalls: Equating the remote sensing operational spectrum with the entire EM spectrum; ignoring that endpoint definitions vary slightly across sources. Final Answer: 10^-10 to 10^10 m

Question 6

In image interpretation for remote sensing, the arrangement of terrain features that conveys attributes such as shape, size, and texture of objects is referred to as:

Accepted Answer

Introduction / Context: Remote sensing imagery is analyzed through multiple cues: spectral, spatial, temporal, and radiometric. Interpreters use these cues to identify land-cover classes, objects, and patterns. Understanding the difference between these dimensions is fundamental to accurate classification and mapping. Given Data / Assumptions: The question points to arrangement-based attributes: shape, size, texture, and pattern. We are not focusing on wavelength-dependent reflectance or time-dependent change. Terminology follows standard image interpretation texts. Concept / Approach: Spatial variation concerns how pixel values and features are arranged in the two-dimensional image plane. It includes geometric properties (shape, size), contextual relationships (pattern, association), and texture (fine vs. coarse). Spectral variation, by contrast, concerns reflectance/emittance differences across wavelengths; temporal variation concerns changes over time; radiometric variation concerns intensity/brightness levels. Step-by-Step Solution: Match the descriptors 'shape, size, texture' to the spatial domain.Exclude spectral (wavelength-based) and temporal (time-based) dimensions.Choose 'Spatial variation' as the correct term. Verification / Alternative check: Standard interpretation keys list tone/color (spectral-radiometric), texture, pattern, shape, size, shadow, site, and association; the latter set belongs to spatial/contextual analysis. Why Other Options Are Wrong: Spectral variation: about different bands/wavelengths, not layout. Temporal variation: about change detection over time. Radiometric variation: about brightness levels, not geometric arrangement. Common Pitfalls: Confusing texture (spatial) with radiometric noise; conflating color (spectral) with spatial pattern. Final Answer: Spatial variation

Question 7

Remote sensing systems primarily utilize which type of waves emitted, reflected, or scattered by Earth surface and atmosphere to sense targets?

Accepted Answer

Introduction / Context: Remote sensing refers to acquiring information about objects or areas from a distance, typically via aircraft or satellites. The vast majority of systems rely on the propagation and interaction of electromagnetic (EM) waves rather than mechanical waves like sound. Given Data / Assumptions: Sensors may be passive (detect reflected sunlight or emitted thermal radiation) or active (radar, lidar) but operate within the EM spectrum. Transmission through the atmosphere depends on wavelength and atmospheric windows. No contact with the target is required. Concept / Approach: Electromagnetic waves include ultraviolet, visible, infrared, microwave, and radio wavelengths. Passive optical sensors record reflected solar radiation; thermal sensors detect emitted radiance; radar systems transmit microwaves and measure backscatter; lidar transmits laser pulses (optical) and records returns. Sound waves (acoustic) are used in sonar (underwater), not in atmospheric remote sensing, and wind waves are surface gravity waves in water, irrelevant to EM-based sensing. Step-by-Step Solution: Identify the physical carrier used by remote sensing sensors.Recognize that both passive and active remote sensing rely on EM radiation.Select 'Electromagnetic waves'. Verification / Alternative check: Sensor families (multispectral, hyperspectral, thermal IR, SAR, lidar) all operate in EM bands, confirming the answer. Why Other Options Are Wrong: Electric waves: imprecise term; EM waves are correct. Sound waves: used in sonar, generally underwater, not for satellite remote sensing of land/atmosphere. Wind waves: hydrodynamic, not a sensing carrier. Seismic waves: used in geophysics, not remote sensing in the EM sense. Common Pitfalls: Confusing sonar (acoustic) with EM-based remote sensing; assuming all 'waves' are interchangeable. Final Answer: Electromagnetic waves

Question 8

Which statements correctly describe fundamental properties of electromagnetic radiation relevant to remote sensing?

Accepted Answer

Introduction / Context: Remote sensing relies on the generation, propagation, and interaction of electromagnetic (EM) waves. Understanding the basic physics of EM radiation clarifies why sensors can operate from aircraft or satellites and still receive information from Earth's surface. Given Data / Assumptions: Classical Maxwellian description of EM fields applies. We consider propagation in free space and in media like air. No special-relativity or quantum details are required. Concept / Approach: Maxwell's equations show that a changing electric field induces a magnetic field and a changing magnetic field induces an electric field, allowing EM waves to be self-sustaining. Because EM radiation does not require a material medium, it propagates through a vacuum—enabling spaceborne observations. The wave comprises perpendicular electric and magnetic components traveling together at the speed of light in vacuum, modified by refractive index in media. Step-by-Step Solution: Confirm coupling of E and B fields (Maxwell-Ampère and Faraday's laws).Note that no medium is required; propagation occurs in space.Affirm that EM radiation consists of both electric and magnetic components.Therefore, all listed statements are correct. Verification / Alternative check: Every remote sensing modality (optical, IR, microwave) depends on this physics; radio communications in space further validate vacuum propagation. Why Other Options Are Wrong: Each single statement is true; the comprehensive choice 'All of these' is appropriate. Common Pitfalls: Assuming EM waves require air to travel; conflating sound wave properties with EM. Final Answer: All of these

Question 9

Which statement best captures what remote sensing measures: interaction and/or emission of electromagnetic radiation from a target?

Accepted Answer

Introduction / Context: Remote sensing captures the radiative signature of targets. This signature arises from how targets interact with incident radiation (reflection, absorption, scattering) and from their own emission (especially in the thermal infrared). Understanding both pathways is essential for interpreting imagery and retrieving geophysical variables. Given Data / Assumptions: Passive optical sensors depend on reflected sunlight. Thermal sensors measure emitted longwave radiation related to temperature and emissivity. Active sensors (radar, lidar) measure returned energy after interaction with the target. Concept / Approach: Targets interact with incoming EM energy via reflection (specular/diffuse), absorption, and scattering, altering the spectrum and intensity recorded by the sensor. In addition, targets emit radiation according to their temperature and emissivity (Planckian behavior for thermal IR). Hence, remote sensing encompasses both interaction with incident radiation and self-emission, depending on wavelength and sensor type. Step-by-Step Solution: Identify key mechanisms: reflection/scattering/absorption and emission.Recognize that sensors capture the net radiance reaching the detector.Conclude that both interaction and emission are relevant and measured. Verification / Alternative check: Thermal IR images at night demonstrate pure emission-based sensing; daytime VNIR images show reflection dominance. Radar (active) measures interaction via backscatter. Why Other Options Are Wrong: Only interaction or only emission is incomplete. 'Neither' contradicts the fundamental operation of remote sensing. 'Only reflection' excludes emission and active sensing returns. Common Pitfalls: Assuming optical remote sensing equals reflection only; ignoring emissivity and temperature effects in thermal imagery. Final Answer: Both (a) and (b)

Question 10

Rayleigh roughness criterion: for a surface to be considered optically rough to incident radiation at wavelength λ and incidence angle θ (from the normal), the root-mean-square height h must satisfy which inequality?

Accepted Answer

Introduction / Context: Surface roughness relative to wavelength controls scattering behavior. In optical and microwave remote sensing, the Rayleigh criterion provides a simple threshold to distinguish between 'smooth' and 'rough' surfaces in terms of phase variations across the surface irregularities. Given Data / Assumptions: λ is the sensing wavelength. θ is the incidence angle measured from the surface normal. h represents a characteristic height (e.g., RMS roughness) of surface irregularities. Concept / Approach: If height variations produce phase differences on the order of π/2 or greater across the illuminated facets, coherent specular reflection breaks down and the surface appears rough. Rayleigh's criterion expresses this as a threshold where h exceeds a fraction of the effective wavelength projected on the surface, commonly given by h > λ/(8 cos θ) for rough classification; for h below this threshold, the surface may be treated as optically smooth for that λ and θ. Step-by-Step Solution: Recall the Rayleigh roughness condition: h_threshold = λ / (8 cos θ).If h > h_threshold, the surface is rough; if h < h_threshold, it is smooth (for the given λ, θ).Identify the option that matches the 'greater than' condition for roughness.Select: h > λ/8 cos θ. Verification / Alternative check: Radar remote sensing texts apply this criterion to predict backscatter regimes (specular vs. diffuse) as a function of wavelength and grazing angle. Why Other Options Are Wrong: Equality or 'less than' does not represent the roughness threshold. Expressions with undefined Δ are not standard. λ/4 cos θ sets a different, stricter threshold than Rayleigh's commonly used 1/8 factor. Common Pitfalls: Forgetting the cosine dependence on incidence angle; applying the criterion with wavelength units inconsistent with h. Final Answer: h > λ/8 cos θ

Question 11

Indian space programme milestones: identify the correct statements about the 1962 initiation, the 1972 creation of the Department of Space (DoS), and the role of the Indian Space Research Organisation (ISRO) in technology and applications.

Accepted Answer

Introduction / Context: India’s space programme has a well-documented timeline: initial organization in the early 1960s, institutional consolidation in the early 1970s, and a mission-focused research organisation tasked with both technology development and national applications. This question checks recognition of those foundational facts used in geography, general studies, and remote sensing syllabi. Given Data / Assumptions: 1962 is cited as the start of the Indian space effort (formation of the national space committee and groundwork for rocket and launch activities). 1972 is associated with the Government of India creating the Department of Space (DoS). ISRO is tasked with space technology development and civilian applications (communications, earth observation, navigation, meteorology, science). Concept / Approach: Interpret each statement as a condensed milestone. The early 1960s mark the organisational beginning; the early 1970s mark the policy and administrative consolidation; ISRO executes missions and applications that translate space technology into public services and scientific gains. If each statement independently matches standard descriptions, the comprehensive option must be correct. Step-by-Step Solution: Check 1962 start: India initiated organized space efforts in the early 1960s, laying the base for sounding rockets and space research.Check 1972 DoS: A dedicated Department of Space was established by the Government of India in 1972 to steer policy and funding.Check ISRO’s role: ISRO develops launch vehicles, satellites, and runs application programmes benefiting communication, agriculture, disaster management, and more.All statements hold true together, so select the combined option. Verification / Alternative check: Compare with standard exam primers and official public sources summarizing India’s space history; the dates and roles align. Why Other Options Are Wrong: Picking any single statement ignores that the others are also correct milestones. Common Pitfalls: Confusing the policy department (DoS) with the executing agency (ISRO). Misreading the 1960s groundwork as later developments. Final Answer: All of these

Question 12

Remote sensing basics: platforms, motion, spatial resolution versus altitude, and area coverage—identify the correct statements about observation geometry.

Accepted Answer

Introduction / Context: Remote sensing acquires information without contact by placing sensors on platforms such as satellites, aircraft, or towers. Platform altitude and motion affect crucial imaging properties like ground sampling distance (spatial resolution) and swath width (area coverage). This question tests foundational definitions and trade-offs. Given Data / Assumptions: Observation location for the sensor is termed the platform. Platforms can be stationary (towers) or mobile (aircraft, spacecraft). Higher altitude generally degrades spatial resolution for a given optics and detector but increases area coverage. Concept / Approach: For a given focal length and detector size, ground sample distance scales approximately with height above ground, thus larger heights yield coarser pixels (poorer resolution). Conversely, instantaneous field of view covers a larger footprint as altitude rises, increasing swath and coverage. Step-by-Step Solution: Define platform: the carrier of the sensor (tower, UAV, aircraft, satellite).Classify mobility: stationary vs mobile is standard.Relate altitude to resolution: higher altitude → larger ground footprint per pixel → poorer spatial resolution, ceteris paribus.Relate altitude to coverage: higher altitude → wider swath → greater area coverage per scene. Verification / Alternative check: Basic imaging geometry shows ground IFOV ≈ H * IFOV_angle; increase in H increases footprint. Why Other Options Are Wrong: Any single statement alone is incomplete; all together accurately describe the relationships. Common Pitfalls: Confusing radiometric resolution with spatial resolution. Assuming higher altitude always worsens resolution even when larger optics can compensate; the statement assumes other parameters fixed. Final Answer: All of these

Question 13

Global Positioning System (GPS) residual error sources: identify which categories of biases affect positional accuracy after basic corrections.

Accepted Answer

Introduction / Context: GPS accuracy is influenced by several residual biases even after applying standard models and corrections. Understanding the taxonomy of errors helps in selecting techniques such as differential GPS (DGPS), real-time kinematic (RTK), or precise point positioning (PPP) to mitigate them. Given Data / Assumptions: Satellite-dependent errors: ephemeris/orbit and satellite clock uncertainties. Receiver-dependent errors: receiver clock stability, multipath susceptibility, hardware delays. Propagation errors: ionospheric and tropospheric delay variability along the path. Concept / Approach: Residual biases can be partitioned by origin: space segment, user equipment, and the propagation medium. Combining dual-frequency measurements, reference-station corrections, and robust hardware mitigates but does not completely remove these effects. Step-by-Step Solution: Identify satellite-dependent terms: orbit/clock errors affect all receivers similarly at a given epoch.Identify receiver-dependent terms: internal clocks and multipath vary user-to-user.Identify propagation terms: ionospheric TEC variations and tropospheric water vapour cause range delays.Since all categories are real contributors, the inclusive option is correct. Verification / Alternative check: Surveying textbooks and GNSS standards list these three classes as principal residuals. Why Other Options Are Wrong: Selecting only one category understates the multifactor nature of GPS error budgets. Common Pitfalls: Conflating multipath (receiver environment) with ionospheric delay (propagation). Ignoring ephemeris updates cadence and precision orbit products. Final Answer: All the above

Question 14

Relief displacement on vertical imagery: two equal-height towers lie 3 km and 5 km from the nadir point on opposite sides. Which statement about their height displacement magnitudes is correct?

Accepted Answer

Introduction / Context: In photogrammetry and remote sensing, relief displacement on a vertical photo causes tall objects to lean radially away from the nadir (principal point). The magnitude of this displacement depends on the object's height and its radial distance from the nadir relative to the flying height. Given Data / Assumptions: Towers A and B have equal heights. Distances from nadir: r_A = 3 km, r_B = 5 km. Both lie on opposite sides of the nadir (direction does not affect magnitude). Flying height H is constant and large compared with object heights. Concept / Approach: The standard relation for radial relief displacement is d = r * h / H, where r is ground radial distance from nadir, h is object height, and H is flying height above ground. For equal h and H, the displacement scales linearly with r. Step-by-Step Solution: Write displacement: d_A = r_A * h / H.Write displacement: d_B = r_B * h / H.Compare using given r values: since r_B > r_A (5 km > 3 km), d_B > d_A.Therefore, tower A's height displacement is less than tower B's. Verification / Alternative check: If r → 0 (at nadir), displacement tends to zero, matching the formula. Increasing r increases displacement, confirming the conclusion. Why Other Options Are Wrong: B < A contradicts the linear r dependence. Equal displacements would require equal r, which is not the case. 'Towards each other' confuses direction with magnitude; in vertical photos, tall objects lean away from nadir on both sides. Common Pitfalls: Mixing up radial distance on the photo with ground distance; proportionality still holds via scale. Forgetting displacement direction is always away from the principal point. Final Answer: Height displacement of A will be less than that of B

Question 15

Soil science terminology: identify the correct statements about soil profile, horizons, and transitional boundaries between horizons.

Accepted Answer

Introduction / Context: Basic pedology (soil science) uses standard terms to describe how soil varies with depth. Examinations often test recognition of the soil profile, its layers (horizons), and the nature of their transitions (boundaries), which are critical for land capability, agriculture, and geotechnical interpretations. Given Data / Assumptions: A vertical cut through soil into parent material reveals distinct layers. Layers broadly parallel to the ground surface are termed horizons (e.g., O, A, E, B, C, R). The interface transition between horizons is termed the boundary. Concept / Approach: The soil profile is the entire vertical sequence from topsoil to parent material; horizons are diagnostic layers with characteristic colour, structure, texture, and chemistry; boundaries describe how sharply or gradually properties change across interfaces. Step-by-Step Solution: Confirm 'profile': full vertical section into parent material.Confirm 'horizons': layers roughly parallel to surface with distinct properties.Confirm 'boundary': the transitional zone between two horizons (abrupt, clear, gradual, diffuse).Since all are standard definitions, choose the inclusive option. Verification / Alternative check: Soil taxonomy manuals and pedology texts employ these exact terms. Why Other Options Are Wrong: Each single statement is correct; excluding any would be incomplete. Common Pitfalls: Confusing a single horizon with the entire profile. Overlooking that boundaries can be wavy, smooth, or irregular and vary in distinctness. Final Answer: All of these

Question 16

Optical oceanography: how does the refractive index of ocean water vary with salinity and temperature (considering pressure constant)?

Accepted Answer

Introduction / Context: The refractive index n of seawater is an important parameter for underwater optics, lidar, and ocean color remote sensing. It influences refraction, Fresnel reflection, and light propagation in the marine environment. Understanding how n changes with water properties helps in sensor calibration and modeling. Given Data / Assumptions: We consider the effect of salinity and temperature at roughly constant pressure. Seawater contains dissolved salts; higher salinity increases density and optical polarizability. Temperature variations affect molecular interactions and density. Concept / Approach: Empirically and via mixing rules, the refractive index of seawater increases with increasing salinity and decreases with increasing temperature (pressure also increases n, but is held constant here). Among the provided single-choice statements, the most directly correct and unambiguous is that n increases with salinity. Step-by-Step Solution: Relate salinity to density and polarizability: higher salinity → higher n.Relate temperature to n: higher temperature generally reduces n (for many liquids) due to lower density.From the given options, select the statement that is certainly true: 'increases with salinity'. Verification / Alternative check: Standard ocean optics references provide parameterizations where n = f(λ, S, T, P) with ∂n/∂S > 0 and ∂n/∂T < 0 at constant pressure. Why Other Options Are Wrong: 'Increases with temperature': opposite sign to typical behavior. 'Decreases with salinity': contradicts observed dependence. 'Decreases with temperature': while often true, the prompt requires one correct choice; the canonical emphasis is salinity increase. Common Pitfalls: Selecting temperature-based statements without specifying pressure and wavelength dependence. Final Answer: increases with salinity

Question 17

Thermal radiation fundamentals: which statements describe an ideal (perfectly) black body's absorption and emission characteristics?

Accepted Answer

Introduction / Context: A perfectly black body is a theoretical construct in thermal radiation and remote sensing. It absorbs all incident electromagnetic radiation and, at thermal equilibrium, emits a characteristic spectrum (Planck distribution). Understanding its properties is crucial for interpreting sensor radiances and calibrations. Given Data / Assumptions: Black body has emissivity ε = 1 at all wavelengths and directions. Diffuse emission means radiance follows Lambert’s cosine law, independent of viewing direction. Emission spans all wavelengths with intensity depending on temperature. Concept / Approach: By definition, a black body absorbs 100% of incident radiation (no reflection or transmission). Kirchhoff’s law links absorptivity and emissivity; an ideal black body is also an ideal emitter. Its spectral exitance follows the Planck function, covering all wavelengths, with peak shifting per Wien’s law. Step-by-Step Solution: Confirm absorption: a black body absorbs all incident radiation.Confirm emission: it emits across the spectrum; the distribution depends on temperature.Confirm diffuse behavior: idealized black surfaces are modeled as Lambertian (diffuse) emitters with directionally uniform radiance.Hence, all listed statements are consistent with the ideal model. Verification / Alternative check: Radiometry texts describe black bodies as perfect absorbers and emitters; laboratory blackbody sources approximate this for sensor calibration. Why Other Options Are Wrong: Any single statement alone is incomplete; black body properties include all three aspects. Common Pitfalls: Confusing 'black paint' with a physical black body; real materials have ε < 1 and may not be perfectly diffuse. Final Answer: All the above

Question 18

Electromagnetic waves: which relationship correctly links wavelength (λ), frequency (f), and propagation speed (C) of an electromagnetic wave in a given medium?

Accepted Answer

Introduction / Context: In remote sensing, optics, and communications, every electromagnetic wave is described by three tightly coupled quantities: its wavelength (λ), its frequency (f), and the speed at which it propagates (C). Recognizing the correct relationship among these parameters is essential for converting between spectral bands, designing antennas, and interpreting sensor data. Given Data / Assumptions: We consider a uniform medium where electromagnetic waves travel with speed C (for example, in vacuum C is approximately 3 * 10^8 m/s). Wavelength λ is the distance between successive crests of the wave, measured in metres. Frequency f is the number of cycles per second, measured in hertz (s^-1). Concept / Approach: By definition, during one period T (seconds) the wave advances one wavelength λ (metres). The frequency is f = 1 / T. The distance covered per second is therefore λ per T seconds, which yields the wave speed C. This fundamental kinematic reasoning gives the core relation that links the three quantities. Step-by-Step Solution: Start from period and frequency: f = 1 / T.Relate distance advanced in one period: distance = λ in time T.Compute speed as distance / time: C = λ / T.Substitute T = 1 / f into C = λ / T to obtain: C = λ * f.Hence the correct relationship among speed, wavelength, and frequency is C = λ * f. Verification / Alternative check: Rearrange the same identity to useful forms: λ = C / f and f = C / λ. These equivalent expressions are widely used to convert between frequency (GHz, MHz) and wavelength (m, cm, mm) for radar, lidar, and optical systems. Why Other Options Are Wrong: C = λ / f: has incorrect units (m / s^-1 = m*s), not speed. C = f / λ: also dimensionally inconsistent (s^-1 / m = 1 / (m*s)). λ = C * f: implies wavelength grows with both speed and frequency; dimensionally wrong (m = m/s * s^-1). f = λ / C: would give units s^-1 = m / (m/s) = s, which is incorrect. Common Pitfalls: Forgetting that in media other than vacuum, C equals the phase speed in that medium (C = c / n), so wavelength changes with refractive index while frequency remains constant across boundaries. Mixing units (e.g., using MHz with metres without converting), which leads to numerical errors even if the formula is right. Final Answer: C = λ * f

Question 19

Coherence condition in wave optics: for two electromagnetic waves to be considered coherent, their phase difference must be what?

Accepted Answer

Introduction / Context: Coherence underpins interference and diffraction phenomena used in optical remote sensing, holography, and laser applications. Exam questions often probe whether you can distinguish temporal coherence (phase stability over time) from spatial coherence (phase correlation across space). Given Data / Assumptions: Two waves are compared at one or more spatial points. Interference visibility requires a well-defined phase relationship during observation. Idealized assumptions ignore noise and turbulence for the conceptual definition. Concept / Approach: Temporal coherence requires the phase difference between two waves at a point to remain constant (or predictable) over the measurement time, enabling stable interference fringes. Spatial coherence concerns correlation of phase at different points in a wavefront. Many textbook definitions test temporal coherence as the minimal condition for two beams to produce steady fringes. Step-by-Step Solution: Identify essential requirement: a constant phase difference in time ensures stationary fringes.Recognize spatial coherence: while important for extended sources, it is not strictly required to answer the basic two-wave coherence condition at one point.Hence, select 'constant in time' as the core condition in many introductory contexts. Verification / Alternative check: Fringe visibility V deteriorates when phase fluctuates in time faster than the detector integration time, demonstrating the centrality of temporal coherence. Why Other Options Are Wrong: 'Constant in space' alone does not guarantee stable interference over time. 'Constant in time and space' is overly restrictive for the basic two-wave condition assessed at a point. 'None of these' contradicts wave optics fundamentals. Common Pitfalls: Confusing requirements for extended-source interferometry (which needs spatial coherence) with the minimal definition for two beams. Final Answer: constant in time

Question 20

Remote sensing instrumentation: devices that emit electromagnetic radiation of a specified wavelength or band to actively illuminate the Earth's surface are called what?

Accepted Answer

Introduction / Context: Remote sensing systems are categorized as passive or active based on whether they rely on external illumination (e.g., the Sun) or generate their own radiation (e.g., radar, lidar). Recognizing this distinction is foundational for understanding data characteristics and use cases. Given Data / Assumptions: Devices provide their own electromagnetic illumination at specific wavelengths or bands. Earth's surface is observed by measuring backscatter or return signal. Examples include synthetic aperture radar (microwave) and lidar (laser). Concept / Approach: Active sensors transmit energy and record the returned signal, enabling night-time and all-weather observations (especially in microwave). Passive sensors record naturally emitted or reflected radiation and cannot be described as 'providing illumination'. Step-by-Step Solution: Match the definition: devices that illuminate the target must be active.Eliminate 'passive sensors': they do not emit, they only detect.Eliminate 'sensonrs': misspelling and not a category.Therefore, select 'active sensors'. Verification / Alternative check: Radar altimeters, scatterometers, and lidars are canonical active systems in Earth observation. Why Other Options Are Wrong: Passive sensors: rely on solar or terrestrial radiation, not on-board illumination. 'sensonrs': not a valid technical term. None of these: incorrect because 'active sensors' is the correct category. Common Pitfalls: Assuming all optical imagers are passive; many lidars operate in optical wavelengths but are active. Final Answer: active sensors

Elements of Remote Sensing Questions