When does a forecast-ensemble twin send the UAV to the wrong place, or make the update worse?

research/targeted-observation-twin

UAV targeted observation planned in a forecast-ensemble twin: exact real error after twin-gain updates, a 2×-too-long correlation length claims −65% and delivers +28% (closed-form harm radius), 10 correct-model members already hurt, localisation and a fitted length scale (m≈50) repair it.

8 tests

What it found

A UAV samples from a corridor to cut forecast error over a region it cannot enter, with sites and Kalman gain taken from a twin’s covariance; the real error after the update is exact (Joseph form, checked against simulation). A matched twin cuts the real error 22%; a twin whose correlation length is 2× too long claims −65% and delivers +28%, because updates are harmful beyond a closed-form radius (ln 2/(ℓ_r⁻²−ℓ_t⁻²))^1/2. Amplitude errors are harmless for one observation but an under-confident twin double-counts over several. A finite ensemble drawn from the correct model already hurts: 10 members give +27% mean real error (71% of ensembles worse than no observation), 50 are safe, and localisation helps at small sizes but costs accuracy at large ones; fitting the length scale from real samples needs about 50. Stylised: 1-D Gaussian field, one static update.

Paper, code and results

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.