Lesson 2 of 6 · Earth observation
Choose the right detail and timing
9 minute lesson · 3 checks along the way
Your goal for this lessonMatch the footprint, sampling interval, and usable coverage to a question about change.
Follow a linked name to explore its archive card. “Back to your lesson” brings you to the same part of the reading.
Words with a dotted underline open a short definition right here in the lesson.
A pixel is a sample, not a promise
concerns the detail a measurement can distinguish. spacing describes how samples are arranged in a product, but it is not a complete statement of resolving power. Optics, detector response, motion, processing, contrast, and noise also matter. A narrow road may influence a pixel without being cleanly resolved as a separate object. Detecting an influence and measuring a shape are different achievements.
Many pixels contain mixtures of land covers. A coastal sample might include water, sand, roofs, and trees. The recorded signal combines their contributions through the instrument’s response. Moving the grid slightly can change those mixtures even when the landscape stays fixed. Before subtracting two images, check their alignment and compare an area large enough for the measurement scale and the intended conclusion.
Resolution has several directions
describes how wavelengths are separated; concerns the encoded signal levels. More encoded levels do not automatically provide better accuracy when calibration or noise dominates. Temporal sampling describes when observations are obtained. A sensor offering finer ground detail may cover a narrower swath or revisit less often. There is no single “highest resolution” product that wins every scientific comparison.
Landsat 8 illustrates why the band matters: its reflected-light multispectral bands have 30-meter sampling, while its thermal bands are acquired at a coarser scale and distributed to a 30-meter grid. Those extra grid locations do not create independent fine-scale thermal measurements. Always distinguish an instrument’s acquisition characteristics from the spacing, , or sharpening applied to a delivered image.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Work through a decision
Count cells and usable dates
Imagine a flat 300-by-300-meter square completely covered by a regular grid, with edges aligned. At 30-meter spacing it contains 10 times 10, or 100 cells. Each covers 900 square meters, so the whole square is 90,000 square meters, or 9 hectares. Resampling the same observations to 10-meter cells produces 900 output cells, not nine times as much independently observed detail.
Now suppose hypothetical visits occur on days 1, 9, 17, and 25. The nominal interval is eight days, but clouds obscure the target on days 9 and 17. The usable clear observations are separated by 24 days. A change visible on day 25 occurred sometime within that bracket; these images cannot pinpoint its date or show whether a brief intermediate event was missed.
A finer grid is not a new observation
Original hypothetical aligned grids. Resampling triples the cell count across each side and gives nine times as many output cells; it adds no independent measurements or guaranteed fine detail.
Open full-size diagram in a new tab: A finer grid is not a new observationCheck 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Choose a question the data can answer
To follow a rapidly changing storm, frequent observations may matter more than resolving a narrow field boundary. To map small parcels, finer spatial information and accurate geolocation may be essential. Radar can provide observations through many clouds, but it measures a different interaction with the surface. Adding radar therefore requires interpretation and suitable validation rather than treating it as an interchangeable clear-sky photograph.
A defensible analysis reports both scheduled opportunities and retained observations after quality filtering. It also records the product grid, effective measurement scale, and any resampling. Missing views remain missing evidence, not observations of “no change.” By comparing the phenomenon’s size and timescale with those limits, you can decide whether to answer the original question, broaden it, or seek another instrument.
Check 3 of 3
10 pointsUse the reading above. You can try again without losing points.
Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
Go to the source
Explore the evidence behind this lesson. These optional readings and videos open in a new tab.