Technology practice questions.

Of the following variables, the one that can be monitored across a whole region by satellite remote sensing rather than by fieldwork is

• the pH of the soil in each field
• the biochemical oxygen demand of a river
• the area of forest cleared each year
• the number of invertebrate species in a stream

Answer: the area of forest cleared each year

Remote sensing records reflected and emitted radiation, so it captures surface properties such as land cover, canopy vigour and surface temperature. Chemical and biological variables inside soil or water still require samples taken and analysed on the ground.

A dissolved oxygen logger holds 200 readings before its memory is full. The record must span a full 24 hours and must resolve the oxygen minimum that occurs shortly before dawn. The setting that meets both requirements is

• one reading every 2 minutes from the moment of deployment
• one reading every 10 minutes from the moment of deployment
• one reading every 3 hours from the moment of deployment
• one reading every 10 minutes, but only during the hours of daylight

Answer: one reading every 10 minutes from the moment of deployment

With 200 readings the interval must be at least 1440 ÷ 200 = 7.2 minutes to span 24 hours, so a 2 minute interval fills the memory in under seven hours, and daylight-only recording misses the pre-dawn minimum altogether. A 3 hour interval spans the day but gives only eight readings, far too coarse to resolve a minimum that lasts an hour or two.

A national bird survey is built from records that volunteers submit through a phone app. The weakness of the resulting data set that is hardest to correct for is that

• the total number of records collected is very small
• records are stored as digital files rather than on paper
• volunteers submit records throughout the year rather than in one season
• recording effort is concentrated near towns and footpaths

Answer: recording effort is concentrated near towns and footpaths

Uneven sampling effort creates apparent hotspots that show where observers went rather than where the birds were, and effort is rarely recorded. Sheer volume of data is normally the strength of citizen science, not its weakness.

Two research groups run climate models for the same emissions scenario and obtain different amounts of warming by 2100. The main reason for the difference is that

• one of the two models must contain an arithmetic error
• the models represent processes such as cloud formation differently
• greenhouse gases behave differently in different countries
• predictions about the future cannot be made with computer models at all

Answer: the models represent processes such as cloud formation differently

A model is a simplification, and small-scale processes such as cloud formation and feedbacks have to be approximated in different ways. The spread between models is a measure of that structural uncertainty, which is why results are reported as a range.

One satellite images any given place at very high spatial detail but revisits it only once every sixteen days; another images the same place every day at much coarser detail. For tracking the day-by-day spread of a flood, the more useful instrument is

• the coarser one, because the flood changes faster than sixteen days
• the detailed one, because spatial detail always outweighs revisit frequency
• neither, because flooding cannot be detected from a satellite
• the detailed one, because floods last for several months

Answer: the coarser one, because the flood changes faster than sixteen days

Choosing a sensor means trading spatial resolution against temporal resolution, and the process being observed decides which matters. A sixteen-day gap can miss a flood entirely, whereas coarse pixels still show where the water is.

Camera traps are deployed to survey the mammals of a forest. Compared with direct observation by a fieldworker, their main advantage is that they

• identify every species automatically without human checking
• record shy and nocturnal animals continuously with no observer present
• give an exact count of the number of individuals living within the area
• work equally well for invertebrates and for small mammals

Answer: record shy and nocturnal animals continuously with no observer present

The camera removes the observer, which removes both the disturbance that keeps shy species away and the limit on how many hours a person can watch. It does not solve identification, and turning images into abundance estimates requires a further method such as individual recognition or occupancy modelling.