Carruthers Data Processing Pipeline: Photon Background Removal
Abstract
The Carruthers Geocorona Observatory, launched in September 2025, is NASA's first mission devoted to investigating the fundamental nature of Earth's exosphere from its distant vantage in halo orbit around the Earth-Sun Lagrange 1 (L1) point. Its primary payload, the GeoCoronal Imager, consists of two coaligned photometric imagers that measure ultraviolet Lyman-alpha emission radiance from exospheric hydrogen simultaneously at wide- and narrow- fields of view. These observations will map the exosphere's global spatial structure and observe its temporal variability in response to geomagnetic storms. However, a critical step in that analysis is isolating the in-band exospheric hydrogen Lyman-alpha signal from any other source of photons, including in-band InterPlanetary Hydrogen photon background and out-of-band photon backgrounds, which are emitted from Earth's limb. This paper details the algorithms used to retrieve and remove photon backgrounds from the GCI science images acquired on-orbit. Finally, the science data processing pipeline that transforms instrument-effect corrected images (L1B science data product) into absolutely-calibrated exospheric H measurements in physical units (L1C science data product) is detailed. Evaluation of algorithm performance based on a realistic pre-flight case study using synthetic data demonstrates that these photon background removal algorithms achieve high accuracy, leaving a residual systematic bias in isolated exospheric Lyman-alpha of only 3% under beginning-of-life conditions.
Related
- An open-source data processing pipeline for Keck / NIRC2-Polarimetry
- Near-Noiseless Single-Photon Detection in the Infrared with a Megapixel Semiconductor Array for Low-Background Astronomy
- Detecting the Axion-Photon Conversion Background
- Analysis of Aditya-L1/VELC [Fe XIV ] 5303 Å Spectroscopic Observations of the Solar Corona: Development of a Data-processing Pipeline
- A data processing pipeline for the WINTER near-infrared surveyor using the mirar framework
BibTeX
@misc{zhang2026carruthers,
title = {{Carruthers Data Processing Pipeline: Photon Background Removal}},
author = {Alex Zhang and Heather Filippini and Jackson Craig and Lara Waldrop and John Clarke and Farzad Kamalabadi and Pratik Joshi},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2606.24030},
eprint = {2606.24030},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.24030},
}
RIS
TY - UNPB
TI - Carruthers Data Processing Pipeline: Photon Background Removal
AU - Alex Zhang
AU - Heather Filippini
AU - Jackson Craig
AU - Lara Waldrop
AU - John Clarke
AU - Farzad Kamalabadi
AU - Pratik Joshi
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2606.24030
UR - https://arxiv.org/abs/2606.24030
AB - The Carruthers Geocorona Observatory, launched in September 2025, is NASA's first mission devoted to investigating the fundamental nature of Earth's exosphere from its distant vantage in halo orbit around the Earth-Sun Lagrange 1 (L1) point. Its primary payload, the GeoCoronal Imager, consists of two coaligned photometric imagers that measure ultraviolet Lyman-alpha emission radiance from exospheric hydrogen simultaneously at wide- and narrow- fields of view. These observations will map the exosphere's global spatial structure and observe its temporal variability in response to geomagnetic storms. However, a critical step in that analysis is isolating the in-band exospheric hydrogen Lyman-alpha signal from any other source of photons, including in-band InterPlanetary Hydrogen photon background and out-of-band photon backgrounds, which are emitted from Earth's limb. This paper details the algorithms used to retrieve and remove photon backgrounds from the GCI science images acquired on-orbit. Finally, the science data processing pipeline that transforms instrument-effect corrected images (L1B science data product) into absolutely-calibrated exospheric H measurements in physical units (L1C science data product) is detailed. Evaluation of algorithm performance based on a realistic pre-flight case study using synthetic data demonstrates that these photon background removal algorithms achieve high accuracy, leaving a residual systematic bias in isolated exospheric Lyman-alpha of only 3% under beginning-of-life conditions.
ER -