Measurement Design Constrains the Use of Landsat Thermal Contrasts for Sustainable Urban-Greening Decisions in Harbin

Urban-greening decisions require interpretable thermal evidence. We analyzed 18 clear-sky summer daytime Landsat 8/9 acquisition groups over Harbin (2022–2025), defining exterior land-surface temperature (LST) contrast as 300–500 m minus 0–200 m around mapped green features. The support-restricted reference retained 73 of 1114 candidates, with an imprecise log-area association (−0.028 °C per original SD; 95% CI, −0.583 to 0.528). An exterior-outcome-aligned analysis retained 271 features; its pooled slope was 0.166 °C (−0.017 to 0.349), whereas direct interaction-model slopes were −0.082 and 0.123 °C without resolved subset heterogeneity. Eligibility changed the analyzed population; a change in the within-subset area association was not established. Built-dominant pseudo-features had a negative median contrast (−0.962 °C), constituting a hot object rather than a neutral design-only benchmark. An exploratory built-fraction-balanced comparison gave a smaller, support-sensitive separation without identifying vegetation-specific cooling. A 224-point mapped-positive audit found 212 Green, two Non-green and ten Uncertain labels; only 13 points belonged to the reference population. Spatial holdout performance was weak (R2 = −0.060). These results support explicit eligibility and background reporting, not causal cooling estimates, optimal park sizes, validated cooling distances or transferable design thresholds.