Notes on calibration, uncertainty, and Earth observation.

SpectraWorks publishes commentary, technical notes, and curated reading on the calibration questions shaping Earth observation. Not every remote sensing problem is a data-access problem - often, the harder question is whether the measurement can be trusted, compared, and defended.

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06 Jul
2026

Technical

Sentinel-3 recalibrated a decade of ocean colour. That is the system working.

On 30 June 2026 EUMETSAT began reprocessing a decade of Sentinel-3 ocean-colour data onto updated calibration. Every prior chlorophyll number moves. Almost nobody noticed. The mechanism behind the quiet correction, and what it says about the sensors that never get one.

SpectraWorks· 7 min read

13 Jun
2026

Commentary

9% or 113%? What a blind test of methane instruments says about unanchored measurement

Eight commercial methane measurement systems were blind-tested against controlled releases in France. On average, their estimates ranged from a tenth of the true emission to slightly more than all of it. The interesting part is not that they disagreed. It is that without the test, nobody could have known.

Richard van Schaik· 4 min read

13 Jun
2026

Commentary

A quality framework, not a calibration standard

In April, NASA, ESA, and USGS released a joint framework for grading the quality of commercial optical satellite data. It is a careful, useful document. It is also advisory. The distance between a framework that documents quality and a reference that provides it is not to be underestimated.

Richard van Schaik· 7 min read

15 May
2026

Commentary

When a regulator asks "how do you know," the answer cannot be a colour ramp

From space, a coffee farm and a forest look the same. The satellite flagged the farm. A Dutch permitting model couldn't prove its own numbers in court. In both cases, a processing chain produced a verdict and had no answer when asked to account for itself.

Richard van Schaik· 8 min read

14 May
2026

Commentary

70% or 7%? The Climate TRACE dispute and the calibration question

When a peer-reviewed paper reports two emissions inventories disagree by 70% across 260 US cities and the dataset producer replies the gap is closer to 6%, the question is not which number is correct. It is how anyone is supposed to know.

Richard van Schaik· 7 min read

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