The phrase "instrumental observations" refers to gathering information or data using tools or devices. It means using instruments or tools to study and collect evidence or facts about a subject. Full definition
This is the heart of climate science: understanding today's climate via instrumental observations and comparing it to the past via proxy data to show how climate has changed over time. (gracelinks.org)
Coral reconstructions extending back centuries provide a link between the period of instrumental observations of the past 50 — 150 years and coarse geological archives that do not relate to human scales. (eos.org)
When used in this way, climate models represent the fundamental physics and chemistry alone, and are not fed information from instrumental observations of the climate system over time — such as the change in atmospheric temperature. (bom.gov.au)