Question 1

Geometric Errors in Satellite Imaging – Which one is random? Among common geometric error sources in satellite images, identify the error that is inherently random rather than systematic.

Accepted Answer

Introduction / Context: Geometric errors in satellite imagery arise from sensor design, platform motion, and Earth geometry. Some are predictable and modeled deterministically, while others vary unpredictably and must be estimated from ancillary data or controlled via stabilization systems. Given Data / Assumptions: Across-track scanning or pushbroom imaging in low Earth orbit. Nominal ephemeris and attitude data are available. We distinguish systematic versus random behaviour. Concept / Approach: Scan skew, panoramic distortion, and Earth rotation effects are systematic and repeatable given the same geometry and timing; they are corrected with known models. Altitude variations caused by atmospheric drag, gravity anomalies, or control jitter introduce non-repeating, random-like deviations in ground projection that require precise orbit determination and possibly ground control points to correct. Step-by-Step Solution: List systematic sources: scan geometry (skew), panoramic distortion, Earth rotation.Identify random source: altitude fluctuations are not perfectly predictable over an image swath.Therefore, altitude variation is the random error among the options. Verification / Alternative check: Operational orthorectification workflows treat the first three with fixed models and consume precise ephemeris/attitude to mitigate random altitude/attitude noise. Why Other Options Are Wrong: They are primarily deterministic functions of scan geometry and timing and thus not random in the sense used in sensor modeling. Common Pitfalls: Confusing repeatable geometric distortions with stochastic platform perturbations; assuming ephemeris alone removes all random components without ground control. Final Answer: Altitude variation (platform height fluctuations)

Question 2

Electromagnetics – Name the law: time-varying E-field generates B-field A time-varying electric field produces a magnetic field. What is this phenomenon called in electromagnetic field theory?

Accepted Answer

Introduction / Context: Maxwell unified electricity and magnetism by adding the displacement current term to Ampere’s circuital law. This addition states that a changing electric field acts like a current and produces a magnetic field, enabling electromagnetic wave propagation even in free space. Given Data / Assumptions: Classical electromagnetic theory in macroscopic form. Time-varying fields; no need for material currents for the effect to exist. Free space or linear media. Concept / Approach: The Ampere–Maxwell law augments Ampere’s law by adding the displacement current density term epsilon * dE/dt. Thus, even where conduction current is absent, a changing electric field produces magnetic field circulation. By symmetry, Faraday’s law states the dual effect: a changing magnetic field induces an electric field. Step-by-Step Solution: Identify the law connecting dE/dt to curl of B: Ampere–Maxwell law.Differentiate from Faraday’s law, which links dB/dt to curl of E.Exclude Kirchhoff’s (circuit laws) and Coulomb’s (electrostatics) as unrelated here. Verification / Alternative check: Wave equation derivation uses both laws; the displacement current term is essential for continuity of current in capacitors and for wave propagation. Why Other Options Are Wrong: Faraday’s law is the magnetic-to-electric counterpart; Hertz verified waves experimentally but did not provide the governing law; Kirchhoff and Coulomb address other regimes. Common Pitfalls: Swapping Faraday’s and Ampere–Maxwell roles; assuming a conduction current is required to generate magnetic fields in time-varying regimes. Final Answer: Ampere–Maxwell law

Question 3

Early Space History – Identify the correct statements Which of the following statements about the earliest Earth-observing and space-imaging milestones are correct?

Accepted Answer

Introduction / Context: Foundational milestones in the Space Age set the stage for today’s Earth observation. Understanding the timeline helps contextualize the evolution from the first artificial satellite to routine meteorological imaging and reconnaissance, which in turn spurred civilian remote sensing missions. Given Data / Assumptions: Basic dates of key missions: Sputnik 1, Explorer 6, TIROS, and CORONA. Focus is on first occurrences and program starts rather than detailed capabilities. Concept / Approach: Sputnik 1 marked the beginning of the Space Age in 1957. Explorer 6 transmitted early images of Earth in 1959. TIROS initiated systematic weather observation by satellite in April 1960. CORONA, a declassified reconnaissance program, began returning film-based imagery around 1960, laying technical groundwork for later civilian imaging systems. Step-by-Step Solution: Check date for Sputnik 1: 4 October 1957.Check Explorer 6: August 1959 Earth image transmission.Check TIROS: first operational meteorological imaging from April 1960.Check CORONA: U.S. reconnaissance imagery acquisition commenced in 1960.All four statements are correct; thus choose “All of these”. Verification / Alternative check: Historical mission summaries and declassified archives corroborate these dates and roles. Why Other Options Are Wrong: Any single statement alone would omit other true milestones, so the combined option is the only fully correct choice. Common Pitfalls: Confusing first satellite (Sputnik 1) with first human in space (Yuri Gagarin, 1961), or mixing TIROS with later NOAA operational constellations. Final Answer: All of these.

Question 4

Specular vs Diffuse Reflection – Which law applies to specular reflection? When a surface reflects radiation in a mirror-like manner (specular reflection), which law does that reflection obey most directly?

Accepted Answer

Introduction / Context: Surface reflection behaviour shapes the appearance of objects in imagery. Two limiting cases are specular reflection (mirror-like) and Lambertian diffuse reflection (equal radiance in all directions relative to surface normal with cosine scaling). Identifying which physical law governs each helps in interpreting glint, water surfaces, and polished materials. Given Data / Assumptions: Incident beam on a smooth surface at an angle to the normal. Wavelength range where geometric optics applies. Idealized specular or diffuse limits for clarity. Concept / Approach: Specular reflection obeys the geometric law that the angle of reflection equals the angle of incidence, both measured in the plane of incidence—commonly associated with Snell’s laws of refraction/reflection at interfaces. In contrast, Lambert’s cosine law describes diffuse reflectors, and Planck’s law governs thermal emission spectra of blackbodies, not reflection. Step-by-Step Solution: Identify the behaviour: mirror-like reflection implies a deterministic outgoing direction.Apply the law: angle of reflection = angle of incidence in the same plane.Exclude alternatives: Lambert (diffuse), Planck (emission), “All/None” are not applicable here. Verification / Alternative check: BRDF models reduce to a delta-like lobe for an ideal specular surface, consistent with Snellian reflection. Why Other Options Are Wrong: Lambert’s law models matte surfaces; Planck’s law concerns emission, not reflection; “All of these” mixes incompatible laws. Common Pitfalls: Confusing specular glint with Lambertian shading; overlooking the plane-of-incidence condition; conflating emission with reflection phenomena. Final Answer: Snell’s law (angle of incidence equals angle of reflection in the plane of incidence)

Question 5

Remote sensing applications: Why are repetitive observations of the same area at equal time intervals critical for monitoring dynamic Earth phenomena?

Accepted Answer

Introduction / Context: Remote sensing missions are designed with a specific temporal resolution, meaning how often a satellite revisits the same ground track. Repetitive observations at equal intervals are essential for monitoring dynamic Earth processes that change over hours, days, or seasons. This question checks whether you recognize the breadth of phenomena that benefit from such time-series imagery. Given Data / Assumptions: Observations of the same area are acquired at consistent time intervals (e.g., daily, 5-day, 16-day). Targets include clouds, vegetation, seasonal snow, and active wildfires. Illumination and atmospheric differences exist but can be normalized with pre-processing. Concept / Approach: Temporal resolution enables change detection. With consistent repeat cycles, analysts compare sequential scenes to quantify trends (e.g., greenness indices), detect anomalies (e.g., sudden burn scars), and characterize diurnal/seasonal cycles (e.g., snowmelt progression). Equal-interval sampling supports robust time-series analysis, filtering, and modeling of dynamic behavior. Step-by-Step Solution: Relate dynamic phenomena to time: clouds evolve hourly; vegetation changes weekly to seasonally; snow expands and retreats seasonally; wildfires can spread within hours to days.Connect repetitive imaging to metrics: NDVI/NDWI trends for vegetation/snow; active fire detections and burn severity; cloud field tracking.Note that equal intervals simplify temporal analytics and reduce aliasing of cycles.Conclude that all listed phenomena benefit significantly from equal-interval monitoring. Verification / Alternative check: Long-running archives (e.g., AVHRR, MODIS, Landsat, Sentinel-2) underlie global vegetation, snow, and fire products precisely because of their repeat cycles and consistent overpass times, confirming the premise. Why Other Options Are Wrong: Cloud evolution: Correct but not exclusive.Vegetative cover: Correct but not exclusive.Snow cover: Correct but not exclusive.Forest fires: Correct but not exclusive. Common Pitfalls: Assuming spatial resolution is always more important than temporal; for dynamic processes, revisit frequency often dominates value. Also, irregular revisit intervals complicate trend analysis. Final Answer: All of these.

Question 6

Optics and photoelectric effect: Identify the correct combined statements about threshold frequency and polarization at Brewster’s angle

Accepted Answer

Introduction / Context: This question blends two cornerstone ideas in optics: the photoelectric effect (quantum threshold) and polarization by reflection (Brewster’s law). It checks whether you can correctly recall the definitions and key geometric property at the polarizing angle for a common medium like glass. Given Data / Assumptions: Photoelectric emission requires photon energy ≥ work function, leading to a threshold frequency. For glass–air interface, the Brewster (polarizing) angle is near 57–58°. At Brewster’s angle, reflected and refracted rays are perpendicular. Concept / Approach: Photoelectric effect: photons with frequency f carry energy hf. If hf is less than the work function, no electrons are emitted—defining a minimum, the threshold frequency. Polarization: Brewster’s law states tan(θ_B) = n_2/n_1. For air-to-glass (n≈1.5), θ_B ≈ arctan(1.5) ≈ 56–57.5°. At θ_B, the reflected light is perfectly plane-polarized, and the reflected and refracted beams are at right angles. Step-by-Step Solution: Map threshold frequency: “minimum frequency for emission” → correct definition.Estimate θ_B for glass: arctan(1.5) ≈ 56–57.5°, so 57.5° is a standard rounded value.Recall geometric property at θ_B: reflected ⟂ refracted rays → orthogonal relationship.Therefore, all three statements hold simultaneously. Verification / Alternative check: Laboratory demonstrations show zero photoemission below threshold regardless of intensity. Glare reduction at the Brewster angle confirms polarization and orthogonality in reflection/refraction geometry. Why Other Options Are Wrong: Any single statement alone is incomplete; the combined option (all) is the most accurate.“None of the above” contradicts established theory and measurements. Common Pitfalls: Confusing intensity thresholds with frequency thresholds; and mixing up Brewster’s angle with critical angle for total internal reflection (a different phenomenon). Final Answer: All the above.

Question 7

Dispersion in optics: Select the correct combined statements about refractive index variation and the prism spectrum

Accepted Answer

Introduction / Context: Dispersion—variation of refractive index with wavelength—underlies many optical effects, from chromatic aberration in lenses to the rainbow spectrum produced by prisms. This question asks you to recognize the standard definitions and the causal link between dispersion and color separation. Given Data / Assumptions: White light contains a continuum of wavelengths. Most transparent media show normal dispersion (n decreases as wavelength increases in the visible range). Prisms refract different wavelengths by different amounts. Concept / Approach: Because n = n(λ), the angle of refraction depends on λ via Snell’s law. Shorter wavelengths (violet/blue) usually experience higher refractive indices and therefore larger deviations than longer wavelengths (red). This wavelength-dependent bending separates white light into its constituent colors. Step-by-Step Solution: Confirm statement a: n varies with λ → true for dispersive media.Confirm statement b: the phenomenon is named “dispersion”.Confirm statement c: prism spectrum is a direct consequence of dispersion.Therefore, all three are correct simultaneously. Verification / Alternative check: Empirical refractometer data show n(λ) curves; ray-tracing through a prism reproduces the color fan consistent with observed spectra. Why Other Options Are Wrong: Any single choice omits part of the full definition–phenomenon linkage.“None” contradicts standard optics. Common Pitfalls: Confusing dispersion with diffraction; prisms separate colors by refraction, not by interference from apertures or gratings. Final Answer: All of the above.

Question 8

Solar spectrum peak: Around which wavelength does the Sun’s radiation reach its maximum intensity (as received at Earth)?

Accepted Answer

Introduction / Context: Understanding where the solar spectrum peaks is fundamental in remote sensing, photovoltaic design, and human vision considerations. The Sun approximates a blackbody emitter near 5770 K, so its spectral irradiance peaks in the visible range near green light. Given Data / Assumptions: Solar effective temperature ≈ 5770 K. Peak intensity reference is the shortwave spectrum at top of atmosphere, with atmospheric effects only slightly shifting ground measurements. Units: micrometre (μm). Concept / Approach: By Wien’s displacement principle, the peak wavelength is λ_max ≈ 2898 μm·K / T. For T ≈ 5770 K, λ_max ≈ 0.50 μm. Accounting for actual solar spectrum and common textbook rounding, many references cite ≈ 0.55 μm (green). Remote-sensing bands and camera sensors are aligned with this visible peak for maximal signal. Step-by-Step Solution: Estimate λ_max using λ_max = 2898 / 5770 ≈ 0.50 μm.Recognize practical peak in extraterrestrial/atmospheric curves appears around 0.50–0.55 μm.Select the standard rounded value 0.55 μm as the best choice.Reject alternatives at 0.40 μm (violet) and 0.70 μm (red) as off-peak. Verification / Alternative check: Solar irradiance standards (AM0/AM1.5) show maximum visible-region energy around green wavelengths, consistent with the 0.5–0.55 μm range. Why Other Options Are Wrong: 0.40 μm: Too short (near violet); intensity is lower than at green.0.70 μm: Too long (red); descending limb of solar curve.1.00 μm: Near-infrared; below the visible peak.None of these: Incorrect since 0.55 μm is appropriate. Common Pitfalls: Confusing human eye sensitivity peak with physical solar peak; fortunately both are close in the green region, aiding daylight vision efficiency. Final Answer: 0.55 μm.

Question 9

Electromagnetic wave velocity in a medium: If permittivity = ε and permeability = μ, what is the wave speed?

Accepted Answer

Introduction / Context: The speed of an electromagnetic (EM) wave in a material medium depends on that medium’s electric permittivity and magnetic permeability. This relationship is a cornerstone of classical electromagnetics and directly connects material properties to propagation speed and refractive index. Given Data / Assumptions: Material characterized by absolute permittivity ε and absolute permeability μ. Losses are negligible (non-conducting, non-dispersive medium) for the basic relation. We refer to phase velocity of a plane EM wave. Concept / Approach: Maxwell’s equations yield the wave equation with wave speed v satisfying v^2 = 1 / (ε * μ). In free space, ε = ε0 and μ = μ0, giving c = 1 / √(ε0 * μ0). In materials, ε and μ alter the speed relative to c, often summarized by refractive index n where n = c / v = √(ε_r * μ_r). Step-by-Step Solution: Start with Maxwell curl equations to derive the homogenous wave equation.Identify that the wave equation constant gives v^2 = 1/(εμ).Take square root for positive speed: v = 1 / √(ε * μ).Relate to refractive index: n = √(ε_r * μ_r) = c / v, as a consistency check. Verification / Alternative check: Plugging ε0 ≈ 8.854×10^-12 F/m and μ0 = 4π×10^-7 H/m yields c ≈ 3×10^8 m/s, matching measured light speed, validating the formula. Why Other Options Are Wrong: εμ or √(ε/μ): Dimensional mismatch for speed.1/(ε*μ): Missing square root; wrong magnitude by many orders.None of these: Incorrect because a standard closed-form exists. Common Pitfalls: Forgetting the square root; confusing relative (ε_r, μ_r) with absolute (ε, μ) values; ignoring frequency-dependent dispersion in real materials (the ideal relation is still foundational). Final Answer: v = 1 / √(ε * μ).

Question 10

Satellite imaging geometry: For across-track sensors, which statements are correct about orbit frame, Earth rotation, and image skew?

Accepted Answer

Introduction / Context: Across-track (whiskbroom or pushbroom) satellite imagers build two-dimensional scenes line by line as the platform moves along its orbit while Earth rotates underneath. This geometry produces systematic effects on ground coverage and image orientation. The question lists three propositions and asks which are correct. Given Data / Assumptions: (1) The satellite orbit is essentially fixed in inertial space over short time scales. (2) During successive scans, Earth rotates beneath the sensor. (3) The imaged ground area is skewed due to relative motion and projection. Concept / Approach: In an inertial frame, a near-polar, Sun-synchronous orbit maintains a nearly fixed plane, while Earth’s rotation causes the ground track to shift west-to-east (or vice versa) between passes, producing revisit patterns. As the sensor scans across track and integrates over finite time, the moving ground imparts a skew or shear to the projected swath unless corrected by onboard timing and ground processing. Step-by-Step Solution: Assess (1): Orbit plane is quasi-inertial (neglecting precession/perturbations) → acceptable for this context.Assess (2): Earth rotation under successive imaging is fundamental to revisit and swath displacement → true.Assess (3): Combined platform motion, scan timing, and Earth rotation yield skewed ground footprints unless rectified → true.Hence, all three statements are correct. Verification / Alternative check: Landsat and Sentinel-2 raw Level-1 products show predictable along-track/scan geometry and require georectification to remove skew and terrain distortions. Why Other Options Are Wrong: Any subset omits a true statement, making it incomplete. Common Pitfalls: Confusing ground-fixed tracks with orbit-fixed planes; assuming images are perfectly north-up without orthorectification. Final Answer: 1, 2, 3.

Question 11

Planetary radiative property: What is the ratio of total solar radiant energy returned by a body to the total radiant energy incident upon it called?

Accepted Answer

Introduction / Context: Radiative terms are often confused in remote sensing and climatology. The question targets the specific planetary-scale quantity used to gauge how bright or dark a body is to incoming solar radiation, integrating over all viewing directions and wavelengths in a defined band. Given Data / Assumptions: Energy considered is solar (shortwave) incident on a planetary body. Returned energy includes reflected and scattered portions. Directional and spectral averaging is implied in the standard definition. Concept / Approach: Albedo is the hemispherical-directional ratio of reflected to incident solar energy, often broadband (0.3–3 μm). It can be defined as Bond albedo (global, all angles) or spherical/planetary albedo. Reflectance is usually a surface-level, narrowband, and geometry-specific property; reflectance factor normalizes reflectance to a Lambertian standard. Step-by-Step Solution: Identify the required ratio: returned (reflected) / incident solar energy.Map terminology: this integrated ratio is albedo.Distinguish from reflectance and reflectance factor, which are geometry/band specific.Select “albedo” as the correct term. Verification / Alternative check: Earth’s mean Bond albedo ≈ 0.30; fresh snow can have albedo > 0.8, deserts ~0.3–0.5, oceans ~0.06–0.1—values widely cited in climate studies. Why Other Options Are Wrong: Reflectance: Often directional and narrowband.Reflectance factor: A normalized reflectance quantity relative to a Lambertian surface.Emissivity: Property for thermal emission, not reflected solar energy.None of these: Incorrect because “albedo” precisely fits. Common Pitfalls: Using “reflectance” when the integrated planetary quantity “albedo” is intended; mixing shortwave (albedo) with longwave (emissivity) concepts. Final Answer: albedo.

Question 12

Cloud microphysics: Under what cloud temperature conditions does snow formation occur?

Accepted Answer

Introduction / Context: Snow formation in clouds depends on the thermodynamic state and microphysical processes, primarily ice nucleation and growth. Knowing the temperature regime for snow is crucial for weather forecasting and interpreting satellite/radar observations of winter precipitation. Given Data / Assumptions: Cloud parcels can be supercooled but still liquid above 0°C depending on nuclei availability. Ice crystal formation generally requires temperatures below 0°C in real clouds. Surface precipitation type can change below the cloud due to melting, but the question addresses formation within the cloud. Concept / Approach: In-cloud snow forms as ice crystals via deposition (vapor to ice), aggregation, and riming. Ice nucleation typically initiates at subfreezing temperatures; heterogeneous nucleation becomes more likely as temperature falls (e.g., below −10°C), while homogeneous freezing of droplets occurs near −38°C. Therefore, snow formation is associated with cloud temperatures below 0°C, even though flakes may encounter warmer layers later. Step-by-Step Solution: Relate snow to ice phase processes → requires T below 0°C for nucleation/growth.Recognize supercooled water can exist slightly below 0°C but does not imply snow formation above 0°C.Conclude that “below the freezing point” best characterizes the temperature regime for snow formation aloft.Reject “at” or “just above” 0°C because liquid phase tends to dominate near the melting level. Verification / Alternative check: Soundings showing dendritic growth zones (around −12 to −18°C) align with prolific snow crystal growth, reinforcing the subfreezing requirement. Why Other Options Are Wrong: Just above/at 0°C: Marginal for ice nucleation; melting dominates.None/Far above 0°C: Contradict the need for ice phase within the cloud. Common Pitfalls: Confusing formation temperature with precipitation type at the ground; melting layers can transform snow to rain before reaching the surface. Final Answer: Below the freezing point.

Question 13

Air photo scale sensitivity: Which factor does NOT affect the scale of vertical aerial photographs?

Accepted Answer

Introduction / Context: The scale of a vertical aerial photograph is the ratio of a photo distance to the corresponding ground distance. It is governed by the camera geometry and the effective flying height over terrain. This question asks which listed factor does not affect scale. Given Data / Assumptions: Vertical (or near-vertical) photography with known focal length f. Flying height above mean terrain H varies with topography. Ground elevation differences cause local scale variation. Concept / Approach: For vertical photos, average scale S ≈ f / H, where H is the flying height above the ground point (not sea level). Thus, focal length directly affects S; greater f increases scale (larger features). Flying height inversely affects scale. Ground elevation changes H locally, altering local scale. Therefore, all three listed factors a–c affect scale, meaning “None of these” is the correct response to “does not affect.” Step-by-Step Solution: Recall S ≈ f / H for vertical photos.Focal length f ↑ ⇒ S ↑ (larger scale).Flying height H ↑ ⇒ S ↓ (smaller scale).Ground elevation modifies local H ⇒ local scale variation across relief.Therefore, none of the listed a–c can be said to “not affect” scale; choose “None of these”. Verification / Alternative check: Relief displacement and scale variation are key reasons for orthorectification; DEMs are used to correct for ground elevation effects on scale and geometry. Why Other Options Are Wrong: Focal length/flying height/ground elevation each demonstrably change scale via S ≈ f/H.Any one of a–c marked as “does not affect” would contradict basic photogrammetry. Common Pitfalls: Confusing atmospheric clarity with geometric scale; while haze affects radiometry, it does not change geometric scale. Final Answer: None of these.

Question 14

Electromagnetic spectrum coverage: Which of the following wavelength domains are part of the EM spectrum?

Accepted Answer

Introduction / Context: The electromagnetic (EM) spectrum spans an enormous range of wavelengths and frequencies, from extremely high-energy gamma rays to low-frequency radio waves. Many remote-sensing instruments and communication systems occupy specific windows within this spectrum. Given Data / Assumptions: Approximate wavelength bounds are used; exact ranges overlap by convention. Statements b and c use inequality cutoffs that include substantial portions of the UV and IR domains, respectively. Radio waves generally include metre-scale and longer wavelengths. Concept / Approach: Despite differing conventional boundaries, the listed domains—gamma, UV, IR, and radio—are indisputably part of the EM spectrum. The inequalities provided are broadly consistent with common textbook partitions (e.g., UV shorter than visible, IR longer than visible up to millimetre and beyond, radio long-wavelength regime). Step-by-Step Solution: Confirm gamma rays occupy the shortest wavelengths (well below 10^-10 m).UV extends below roughly 4×10^-7 m; “< 10^-6 m” certainly covers UV and more.IR spans ~0.7 μm to 1 mm; “< 10^-4 m” captures near/mid IR portions.Radio waves include wavelengths greater than 1 m among many bands.Therefore, all listed domains belong to the EM spectrum. Verification / Alternative check: Standard EM spectrum charts show continuous coverage across these regions; instrument bands (e.g., thermal IR ~10 μm, L-band radar ~23 cm) sit within the stated ranges. Why Other Options Are Wrong: Any single selection would ignore the fact that all mentioned categories are genuine EM regions. Common Pitfalls: Over-interpreting the inequalities as exact definitions; boundaries are conventional and application-dependent but do not change membership in the EM spectrum. Final Answer: All of these.

Question 15

GPS receivers — what clock type do they actually use? In practical Global Positioning System (GPS) field equipment, which type of timing reference is used inside the receiver unit to time-stamp and correlate the satellite codes (while the satellites…

Accepted Answer

Introduction / Context: Precise timing is the heart of satellite navigation. GPS positioning works by measuring how long a coded radio signal takes to travel from a satellite to the receiver. Although nanosecond-level timing stability is required in the space segment, the design choices for user receivers are very different because of cost, size, and power constraints. Given Data / Assumptions: GPS satellites carry highly stable time references. User receivers correlate pseudorandom (PRN) codes to estimate signal travel time. Receivers must be economical, compact, and low power for mass deployment. Concept / Approach: Satellites house atomic clocks (cesium, rubidium) that broadcast time-tagged signals. Receivers do not need on-board atomic clocks; instead they use temperature-compensated crystal oscillators (TCXO/OCXO) based on quartz. Any residual receiver clock bias is solved as an unknown in the navigation solution alongside the three position coordinates, which is why at least four satellites are required for a stand-alone fix. Step-by-Step Solution: 1) Satellite signals include precise timing derived from atomic standards.2) Receiver uses a quartz oscillator to track and correlate PRN codes.3) Clock bias (receiver vs. GPS time) is estimated during positioning; no atomic clock is needed in the receiver.4) Therefore, among the options, the correct receiver clock type is quartz. Verification / Alternative check: Receiver specification sheets list TCXO/OCXO quartz oscillators. Survey-grade units may offer better-stability quartz or external disciplining (e.g., to GNSS time) but still not internal atomic clocks in normal operation. Why Other Options Are Wrong: Atomic clocks are on satellites and in specialized timing labs, not standard field receivers. “Electronic clocks” is vague and non-specific. Mechanical clocks cannot provide the required frequency stability. Common Pitfalls: Assuming receivers must mirror satellite atomic stability; they exploit multi-satellite geometry to estimate clock bias instead. Confusing disciplining to GPS time with housing an atomic standard. Final Answer: Quartz clocks.

Question 16

Digital cartography — which attribute is NOT typical of a digital map? Digital maps routinely include color/colour schemes, standardized symbology, and explanatory legends. Which of the following is NOT a standard attribute associated with digital m…

Accepted Answer

Introduction / Context: Map design uses a consistent visual language so users can read geometry and attributes reliably. Three foundational elements in both analog and digital cartography are colour palettes, symbology, and legends. Orientation cues are also used—but in a specific, widely accepted way. Given Data / Assumptions: We are considering standard topographic/thematic digital maps. Orientation is conventionally indicated with a north arrow or by a graticule. Terminology should match common cartographic practice. Concept / Approach: Colour conveys qualitative and quantitative differences; symbology encodes feature classes and statuses; legends explain this encoding to the reader. Orientation is normally indicated by a north arrow (or grid/true-north references). A “south arrow” is not a recognized convention and would likely confuse users unless a very unusual, clearly explained design is used. Step-by-Step Solution: 1) List typical attributes: colour, symbology, legend—each is standard.2) Orientation indicator: by convention a north arrow, not a south arrow.3) Therefore the nonstandard attribute is “south arrow”. Verification / Alternative check: Cartography textbooks and GIS software defaults (e.g., map layout tools) provide north arrows and legend builders; “south arrow” does not appear as a standard element. Why Other Options Are Wrong: Colour, symbology, and legends are essential components of readable maps. Common Pitfalls: Confusing “legend” with “table of contents/layer list”; many tools show both. Overusing colour without adequate contrast or accessibility checks. Final Answer: South arrow.

Question 17

Electromagnetic radiation — identify the incorrect statement Which one of the following statements about the origin and coupling of electromagnetic (EM) fields is incorrect?

Accepted Answer

Introduction / Context: Electromagnetic radiation emerges from time-varying electric charges and currents. Maxwell’s equations link electric and magnetic fields so that changes in one generate the other, enabling wave propagation through space (and many media) without a material carrier. Given Data / Assumptions: Classical EM theory in free space or simple media. Non-relativistic descriptions are adequate for these qualitative statements. We are testing conceptual correctness, not numerical computation. Concept / Approach: Accelerating charges and time-varying currents produce time-varying electric and magnetic fields. Faraday’s law links changing magnetic flux to induced electric fields; Maxwell-Ampère’s law links changing electric fields (displacement current) and currents to magnetic fields. Together these form coupled wave equations describing EM radiation. Hence statements (a)–(c) correctly summarize fundamental physics; there is no incorrect choice among them, so “None of these” is the correct selection for “which is incorrect?”. Step-by-Step Solution: 1) Evaluate (a): moving/accelerating charges radiate ⇒ correct.2) Evaluate (b): oscillating charges create time-varying E-fields ⇒ correct.3) Evaluate (c): time-varying E-fields induce B-fields (Maxwell–Ampère) ⇒ correct.4) Therefore none of (a)–(c) is incorrect → choose “None of these”. Verification / Alternative check: Deriving the wave equation from Maxwell’s equations yields ∇^2E − μϵ ∂^2E/∂t^2 = 0 and the analogous form for B, confirming mutual coupling and propagation. (Symbolic mention only; no detailed math required here.) Why Other Options Are Wrong: Selecting any of (a)–(c) as incorrect would contradict Maxwellian electrodynamics. Common Pitfalls: Assuming constant-velocity charges radiate; radiation requires acceleration. Imagining E or B can exist independently in a propagating wave; in free space they are coupled and transverse. Final Answer: None of these.

Question 18

GPS signal structure — what do satellites transmit and how is range measured? Which consolidated statement about GPS L-band signals, satellite PRN codes, and receiver ranging is correct?

Accepted Answer

Introduction / Context: Understanding how GPS measures distance helps explain both its strengths and its error sources. Satellites broadcast coded L-band signals that receivers decode to separate satellites and to determine the apparent signal travel time, which is then converted into pseudorange. Given Data / Assumptions: Classical GPS description (L1, L2; modern systems add L5 and new codes). Receivers correlate PRN codes to estimate delay. Distance is derived from signal travel time multiplied by the speed of light, corrected within the navigation solution. Concept / Approach: Each satellite has unique PRN codes modulating the L-band carrier(s). Code correlation in the receiver determines the code phase offset, which corresponds to the signal transit time (plus biases). Multiplying by the speed of light yields a pseudorange; with multiple satellites, the receiver solves for position and clock bias. Step-by-Step Solution: 1) Satellites transmit L-band carriers (traditionally two: L1 and L2).2) Carriers are modulated with PRN codes (e.g., C/A, P(Y)).3) Receiver locks onto a specific satellite by its PRN identity.4) Code phase → time delay → pseudorange → position solution. Verification / Alternative check: Any GPS fundamentals text shows L1/L2 with PRN coding and the correlation process for ranging. Modernized signals (e.g., L5) extend but do not change the basic principle. Why Other Options Are Wrong: Options (a)–(d) are individually correct; hence the combined correct choice is “All of these”. Common Pitfalls: Confusing carrier phase tracking (much more precise) with code-phase ranging. Forgetting that ranges are “pseudo” because of clock and media delays. Final Answer: All of these.

Question 19

Ocean colour & phytoplankton — apparent water colour in sunlight Water that is rich in phytoplankton typically appears what colour to the human eye under sunlight, and why?

Accepted Answer

Introduction / Context: Remote sensing and ocean optics relate water colour to the substances in the water column, notably phytoplankton, coloured dissolved organic matter (CDOM), and suspended sediments. Chlorophyll-a in phytoplankton strongly absorbs parts of the visible spectrum, which changes the apparent colour seen from above. Given Data / Assumptions: Sun-lit conditions; observation by eye or broad-band sensors. Phytoplankton contain chlorophyll-a and accessory pigments. No extreme sediment or CDOM dominance masking the signal. Concept / Approach: Chlorophyll-a absorbs strongly in the blue (~0.44 μm) and red (~0.67 μm) and reflects/scatters more in the green band. Thus, as phytoplankton concentration increases, water tends to shift from deep blue (oligotrophic) toward green hues (eutrophic), all else equal. Brown hues are more typical of high suspended sediment, while red is unusual except during specific blooms or optical illusions at low sun angles. Step-by-Step Solution: 1) Identify dominant absorber: chlorophyll-a.2) Note spectral absorption: high in blue and red → less reflected.3) Remaining reflectance peaks nearer green → perceived green colour. Verification / Alternative check: Standard ocean colour algorithms (e.g., band ratios including green) exploit this spectral behavior to estimate chlorophyll concentration from satellite data. Why Other Options Are Wrong: Blue corresponds to clear, low-chlorophyll waters. Brown often indicates sediments or humic substances. Red is atypical; certain blooms can redden water but are exceptions. Common Pitfalls: Confusing sediment-driven colour changes with phytoplanktonic signals. Ignoring the role of sun angle and sky reflection at glint angles. Final Answer: Green.

Question 20

Ocean optics — scattering, colour, and reflectance ratio Which consolidated statement correctly describes short-wavelength scattering in seawater and a standard reflectance definition?

Accepted Answer

Introduction / Context: Why the open ocean looks blue—and how we quantify the light field—are fundamental topics in marine optics. The balance between molecular/small-particle scattering and absorption sets the water colour, while radiometric ratios standardize how we compare optical states across sites and times. Given Data / Assumptions: Clear oceanic water with low suspended sediment and CDOM. Standard definitions of upwelling and downwelling irradiance. Shorter wavelength means violet–blue bands of visible light. Concept / Approach: Rayleigh-like scattering by water molecules and small ions increases as wavelength decreases, so blue light is scattered/backscattered more effectively than red. In clear waters, absorption is low in blue, so enhanced backscatter yields the characteristic deep blue appearance. The irradiance reflectance is defined as R = Eu(0−)/Ed(0+), i.e., upwelling irradiance just below the surface divided by downwelling irradiance just above the surface, a common metric in ocean color research. Step-by-Step Solution: 1) State wavelength dependence: shorter λ → stronger scattering.2) Link to appearance: more blue backscatter → blue ocean colour.3) Provide radiometric definition: R = Eu(0−) / Ed(0+). Verification / Alternative check: Textbook spectral curves show minimal absorption in the blue for pure water and increasing absorption toward red/IR, supporting the colour mechanism and the usefulness of blue-band reflectance metrics. Why Other Options Are Wrong: Each of (a)–(c) is correct; hence the combined correct choice is “All of these”. Common Pitfalls: Confusing irradiance reflectance with remote-sensing reflectance R_rs, which uses radiance rather than irradiance. Ignoring CDOM/sediment effects that can shift colour toward green/brown. Final Answer: All of these.

Elements of Remote Sensing Questions