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Concepts

This page covers the key ideas behind the S2GOS Observation Simulator: spectral modes, how atmosphere interacts with measurements, and the available sensor types.

Spectral Modes

The simulator uses Eradiate as its radiative transfer backend. Eradiate operates in a spectral mode that determines how wavelength integration and gas absorption are handled. The mode is set via backend_hints in the simulation config:

backend_hints={"mode": "ckd"}

Sensors

The simulator supports three platform types, each with different instrument options and viewing geometries.

Satellite

Satellite sensors produce 2D imagery at a specified ground resolution. Two main instrument categories:

  • MSI (MultiSpectral Instrument) — Few broad bands. Sentinel-2A/2B. Each band is simulated independently with its spectral response function.
  • HSI (HyperSpectral Instrument) — Hundreds of narrow contiguous channels such as teh guture CHUME mission. Gaussian SRF post-processing simulates the instrument's spectral response.

Built-in satellite platforms: Sentinel-2A/2B, Sentinel-3A/3B, CHIME (approcimation), EnMAP. Custom platforms are supported with user-provided SRFs.

CKD mode is recommended for all satellite instrument simulations.

UAV

UAV sensors are placed at a specified altitude with a configurable viewing geometry:

  • Perspective camera — 2D imaging with a field of view and film resolution
  • Radiancemeter — Single-point radiance measurement

Ground

Ground-based sensors are placed at low heights for in-situ validation measurements:

  • HYPSTAR — HYPERNETS network sensor. Circular FOV, approximate SRF
  • Perspective camera — Standard camera with configurable FOV
  • Radiancemeter — Directional radiance measurement

See the Sensors API reference for full configuration details and helper functions like create_chime_sensor() and create_hypstar_sensor().