Oceanography & Hydrology

What specific physical property does the GRACE satellite measure to infer changes in groundwater and ice mass?

Variations in Earth's gravity field caused by changing mass distributions.

In the context of GRACE data, what does a negative gravity anomaly in Greenland typically indicate?

A loss of ice mass (melting), often expressed as "equivalent water height" loss.

What are the two primary instruments onboard the GPM (Global Precipitation Measurement) Core Observatory?

The Dual-frequency Precipitation Radar (DPR) and the GPM Microwave Imager (GMI).

The GPM's Dual-frequency Precipitation Radar (DPR) operates in which two microwave bands?

Ku-band (13.6 GHz) and Ka-band (35.5 GHz).

Why does the GPM Core Observatory use a non-sun-synchronous orbit with an inclination of 65 degrees?

To sample precipitation across all local times of day (diurnal cycle) rather than passing over at the same local time every day.

What is the primary variable measured by satellite altimeters like Jason-3 and Sentinel-6 Michael Freilich?

Sea Surface Height (SSH) relative to a reference ellipsoid.

What specific "correction" must be applied to radar altimetry data to account for the slowing of radar pulses by atmospheric moisture?

The "Wet Tropospheric Correction."

In the context of the PACE mission, what is the OCI and what makes it "hyperspectral"?

The Ocean Color Instrument; it measures light at 5 nm intervals across a broad spectrum rather than just a few discrete bands.

What specific biological measurement is the PACE satellite designed to differentiate that previous satellites could not?

Phytoplankton community composition (identifying specific types/species of algae rather than just total chlorophyll).

Which satellite mission is best suited for measuring "sea surface salinity" (SSS)?

SMAP (Soil Moisture Active Passive) or the retired Aquarius mission.

During an El Niño event, how does the "Walker Circulation" change?

It weakens or reverses, causing the main region of rising air and convection to shift from the Western Pacific toward the Central/Eastern Pacific.

On a map of Sea Surface Height (SSH) anomalies, what feature indicates a "Warm Core Eddy"?

A circular region of positive height anomaly (a "hump" of water), since warm water is less dense and takes up more volume.

What is "Thermal Expansion" and roughly what percentage of modern sea level rise does it account for?

The increase in water volume as it warms; it accounts for roughly 30-50

of current global sea level rise.

How does the "Ice-Albedo Feedback" loop contribute to "Arctic Amplification"?

Melting ice reveals darker ocean water, which has a lower albedo and absorbs more solar energy, leading to further warming and melting.

What is the "Antarctic Circumpolar Current" (ACC) and why is it unique?

It is the largest ocean current and the only one that flows completely around the globe without being blocked by land.

What distinct spectral signature allows remote sensors to distinguish between "clouds" and "snow/ice" in the Shortwave Infrared (SWIR) bands?

Snow/ice absorbs strongly in the SWIR (appears dark), while water clouds remain highly reflective (appear bright).

What does a "scatterometer" (like on QuikSCAT) measure over the ocean?

Ocean surface wind speed and direction (by measuring the backscatter or "roughness" of capillary waves).

During a La Niña phase, how does the thermocline depth change in the Eastern Equatorial Pacific?

The thermocline becomes shallower (rises closer to the surface), often breaking the surface and increasing cold water upwelling.

What is the "Red Edge" in spectral analysis, and how can it be used in oceanography?

The sharp increase in reflectance between red and Near-Infrared; in oceans, it helps identify floating vegetation or intense algal blooms.

The "A-Train" satellite constellation is designed to fly in close formation to allow for what type of observation?

Coincident (simultaneous) measurements of the same Earth scene by multiple instruments.

What is "Sun Glint" in optical satellite imagery?

The specular reflection of the sun off the water surface; it can reveal oil spills or surface roughness patterns.

In the context of the Earth's Energy Budget, what is "Radiative Forcing"?

The difference between incoming solar energy and outgoing terrestrial energy (measured in Watts per square meter).

Which specific greenhouse gas is the OCO-2 (Orbiting Carbon Observatory-2) designed to map?

Carbon Dioxide (CO2).

What is the primary "sink" for anthropogenic Carbon Dioxide that PACE aims to study?

The Ocean Biological Pump (phytoplankton photosynthesis and subsequent sinking of organic matter).

How does "Colored Dissolved Organic Matter" (CDOM) affect the spectral reflectance of ocean water?

CDOM strongly absorbs blue light, making the water appear darker or more yellow/brown.

What is the "Kelvin Wave" in the context of ENSO onset?

A massive pulse of warm subsurface water that travels eastward across the Pacific Equator, deepening the thermocline and initiating El Niño.

What is "Geostrophic Flow" in oceanography?

Ocean currents that result from a balance between the pressure gradient force and the Coriolis effect.

Which NASA satellite instrument provides the longest continuous record of stratospheric ozone and atmospheric trace gases?

OMI (Ozone Monitoring Instrument) on the Aura satellite.

What is the difference between "active" and "passive" remote sensing instruments used in hydrology?

Active sensors emit their own energy pulse (e.g., Radar); Passive sensors measure naturally reflected sunlight or emitted heat.

In an infrared satellite image of a hurricane, what does a "cold ring" surrounding a warmer center indicate?

The "Eye Wall"—the area of strongest convection and tallest clouds surrounding the eye.

What is "Altimetric Bathymetry"?

Inferring ocean floor topography by measuring small gravitational bulges in the sea surface height using radar altimeters.

How does the "Stefan-Boltzmann Law" apply to infrared ocean sensing?

It relates the total energy emitted by the ocean surface to its temperature, allowing radiometers to calculate Sea Surface Temperature.

What is the "Intertropical Convergence Zone" (ITCZ) and how does it appear on satellite imagery?

A band of persistent clouds and thunderstorms near the equator where trade winds converge.

What is the primary advantage of using "Synthetic Aperture Radar" (SAR) for monitoring sea ice?

SAR can see through clouds and darkness and can distinguish ice texture/roughness.

What does the acronym "NDWI" stand for and what is it used to map?

Normalized Difference Water Index; used to delineate open water features and enhance the presence of water in satellite imagery.

Which satellite constellation is specifically responsible for maintaining the reference record for global sea level rise?

The Sentinel-6 / Jason series.

What is an "Atmospheric Window" in remote sensing?

Specific ranges of wavelengths (e.g., 8-12 micrometers) where the atmosphere is transparent, allowing satellites to measure surface temperature.

During an El Niño event, what happens to the biological productivity off the coast of Peru?

It collapses because the deep, nutrient-rich cold water is prevented from upwelling by the layer of warm surface water.

What is the "swath width" of the GPM Microwave Imager (GMI) compared to the Radar (DPR)?

The GMI has a much wider swath (~885 km) compared to the DPR (~245 km), allowing broader coverage.

What role do "Aerosols" play in the Earth's energy budget?

They can directly reflect/absorb sunlight and indirectly cool the Earth by making clouds brighter (Twomey Effect).

What is "Euphonic Depth" (or Photic Zone)?

The depth to which sunlight penetrates ocean water, allowing photosynthesis to occur.

What are the "Doldrums"?

The region near the equator with very light ocean winds where the trade winds converge; detectable by scatterometers as areas of low surface roughness.

How does "Salinity" affect the dielectric constant of water?

Higher salinity increases the dielectric constant, changing the emissivity, which allows passive microwave radiometers to measure salinity.

What is a "Lagrangian" drifter (like in the Argo program) vs. a satellite measurement?

A drifter physically moves with the water parcel (in situ), while a satellite takes a snapshot from a fixed frame above.

What is "Glacial Isostatic Adjustment" (GIA)?

The ongoing rise of land masses that were depressed by the weight of ice sheets during the last ice age.

What is the "Signal-to-Noise Ratio" (SNR) and why is it critical for PACE?

It is the ratio of useful data to background noise; PACE requires high SNR to detect subtle color differences between phytoplankton species.

What is "Lidar" and which satellite used it to measure cloud vertical structure?

Light Detection and Ranging; CALIPSO used lidar to measure cloud altitude and aerosol layers.

What is the "Greenhouse Effect" in terms of spectral transmission?

The atmosphere is transparent to incoming shortwave radiation but absorbs outgoing longwave radiation, trapping heat.

What is the primary difference between "Sea Ice" and "Ice Shelves"?

Sea ice forms from freezing ocean water; Ice shelves are floating extensions of land-based glaciers.

What is "Ocean Acidification" and how can remote sensing indirectly monitor it?

The decrease in ocean pH due to CO2 uptake; monitored by tracking the biological carbon pump.