Advanced Hyperspectral Imager

Overview

The Advanced Hyperspectral Imager (AHSI) is a spaceborne pushbroom hyperspectral sensor covering 387-2,516 nm across 330 spectral bands at 30 m ground sampling distance (GSD) and 60 km swath.^[1] It was first flown on GaoFen-5, launched 2018-05-09 and since decommissioned.^[2] The same AHSI design also flies on the operational GaoFen-5-02, launched 2021-09-07.^[3] A hyperspectral imager of the AHSI lineage also flies on GaoFen-5-01A, whose detailed spectral configuration is not confirmed in peer-reviewed sources.^[3]

Spectral design

AHSI uses two separate pushbroom spectrometers sharing a common telescope.^[1] The VNIR spectrometer covers 387-1,024 nm with 150 bands at approximately 5 nm spectral sampling. The SWIR spectrometer covers 1,009-2,516 nm with 180 bands at approximately 10 nm spectral sampling.^[1] The 387 nm lower bound and 2,516 nm upper bound are from the primary instrument characterisation paper; commonly cited figures of 400 nm and 2,500 nm are rounded approximations.^[1] Signal-to-noise ratio has been characterised at approximately 700 in the VNIR and approximately 500 in the SWIR.^[1]

The optical design uses a convex-grating approach for the VNIR and an Offner three-concentric-mirror configuration for the SWIR, a combination that minimises smile and keystone distortion across the focal plane.^[1]

Observation applications

Hyperspectral classification of land-cover classes has been demonstrated using AHSI data from GaoFen-5.^[1] Spectral library matching for lithological mapping has been demonstrated from GaoFen-5 AHSI imagery.^[4] Spectral unmixing for sub-pixel material decomposition has been demonstrated using AHSI data.^[4] Gas plume detection via matched-filter methods is capable given AHSI spectral coverage and resolution, though published demonstrations on operational retrievals from this specific instrument remain limited.^[1]