Satellite ocean color sensors measure chlorophyll-a concentration in surface waters. Why is this measurement significant for understanding ocean productivity?
AChlorophyll-a is a pollutant that indicates water quality degradation
BChlorophyll-a is the primary photosynthetic pigment in phytoplankton, so its concentration is a proxy for phytoplankton biomass and primary productivity -- the base of the marine food web
CChlorophyll-a concentration directly measures fish populations
DChlorophyll-a indicates water temperature more accurately than thermal sensors
Phytoplankton are responsible for roughly half of global photosynthesis. Chlorophyll-a, detected through its absorption of blue and red light and reflectance of green, serves as a quantitative proxy for phytoplankton abundance. Mapping chlorophyll from space reveals bloom dynamics, upwelling zones, nutrient transport, and the ocean's biological response to climate variability.
Question 2 True / False
Radar altimeters measure sea surface height by timing radar pulses reflected from the ocean surface. This measurement is only useful for studying tides.
TTrue
FFalse
Answer: False
Sea surface height variations encode a wealth of information beyond tides: ocean currents (geostrophic flow is proportional to the surface height gradient), mesoscale eddies, El Nino/La Nina events, global sea level rise (measured at ~3.3 mm/year by satellite altimetry since 1993), and even marine gravity anomalies that reveal seafloor topography. Altimetry has been transformative for physical oceanography.
Question 3 Short Answer
Explain why microwave sensors are used for global SST measurement in addition to infrared sensors, given that infrared has better spatial resolution.
Think about your answer, then reveal below.
Model answer: Infrared SST measurements are blocked by clouds, and much of the ocean is persistently cloudy (particularly high latitudes and tropical convergence zones). Passive microwave sensors (like AMSR-E) operate at wavelengths that penetrate clouds, providing all-weather SST coverage, though at coarser spatial resolution (~25 km vs ~1 km for infrared). Blended SST products combine infrared data (high resolution where clear) with microwave data (filling cloud gaps) to produce complete daily global SST maps.
Infrared gives sharp detail where skies are clear; microwave gives continuous coverage through clouds. The complementarity is essential for complete ocean monitoring.