The Methane Isotopologues by Solar Occultation (MISO) Nanosatellite Mission: Spectral Channel Optimization and Early Performance Analysis

Landgraf

et al. 2019

Atmos. Meas. Tech.

Abstract. Retrievals of methane isotopologues have the potential to differentiate between natural and anthropogenic methane sources types, which can provide much needed information about the current global methane budget. We investigate the feasibility of retrieving the second most abundant isotopologue of atmospheric methane (13CH4, roughly 1.1 % of total atmospheric methane) from the shortwave infrared (SWIR) channels of the future Sentinel-5/ultra-violet, visible, near-infrared, shortwave infrared (UVNS) and current Copernicus Sentinel-5 Precursor TROPOspheric Monitoring Instrument (TROPOMI) instruments. With the intended goal of calculating the δ13C value, we assume that a δ13C uncertainty of better than 1 ‰ is sufficient to differentiate between source types, which corresponds to a 13CH4 uncertainty of <0.02 ppb. Using the well-established information content analysis techniques and assuming clear-sky, non-scattering conditions, we find that the SWIR3 (2305–2385 nm) channel on the TROPOMI instrument can achieve a mean uncertainty of <1 ppb, while the SWIR1 channel (1590–1675 nm) on the Sentinel-5 UVNS instrument can achieve <0.68 ppb or <0.2 ppb in high signal-to-noise ratio (SNR) cases. These uncertainties combined with significant spatial and/or temporal averaging techniques can reduce δ13C uncertainty to the target magnitude or better. However, we find that 13CH4 retrievals are highly sensitive to errors in a priori knowledge of temperature and pressure, and accurate knowledge of these profiles is required before 13CH4 retrievals can be performed on TROPOMI and future Sentinel-5/UVNS data. In addition, we assess the assumption that scattering-induced light path errors are cancelled out by comparing the δ13C values calculated for non-scattering and scattering scenarios. We find that there is a minor bias in δ13C values from scattering and non-scattering retrievals, but this is unrelated to scattering-induced errors.

Section: Discussionmentioning

confidence: 99%

A study of synthetic 13CH4 retrievals from TROPOMI and Sentinel-5/UVNS

Landgraf

et al. 2019

Atmos. Meas. Tech.

“…Nisbet et al (2016) identify that for a given source type δ 13 C values typically vary by up to 1‰ over the course of a year, which means that TROPOMI/Sentinel 5/UVNS need to achieve 1‰ total uncertainty or better (<0.1‰, if seasonal variations are to be observed (Nisbet et al, 2016). However Buzan et al (2016), Weidmann et al (2017) and Malina et al (2018) identify that with current satellite retrieval techniques, this level of precision is unlikely to be achievable, since this would require total 13 CH 4 column errors <0.02 ppb, which equates to roughly 0.1% 13 CH 4 total column error; which is not currently possible even for higher concentration species. The question then becomes, what may be technically possible with current satellite instruments, and how such data can be leveraged.…”

Section: Study Requirementsmentioning

confidence: 99%

A study of synthetic 13CH4 retrievals from TROPOMI and Sentinel 5/UVNS Part 1: non scattering atmosphere

Landgraf

et al. 2019

Preprint

Abstract. Retrievals of methane isotopologues have the potential to differentiate between natural and anthropogenic methane sources types, which can provide much needed information about the current global methane budget. We investigate the feasibility of retrieving the second most abundant isotopologue of atmospheric methane (13CH4, roughly 1.1 % of total atmospheric methane) from the Shortwave Infrared (SWIR) channels of the future Sentinel 5/UVNS and current Copernicus Sentinel 5 Precursor TROPOMI instruments. With the intended goal of calculating the δ13C ratio, we assume that a δ13C uncertainty of better than 10 ‰ is sufficient to differentiate between source types, which corresponds to a 13CH4 uncertainty of <0.2 ppb. Using the well established Information Content analysis techniques and assuming clear sky, non-scattering conditions, we find that the SWIR3 (2305–2385 nm) channel on the TROPOMI instrument can achieve a mean uncertainty of <1 ppb, while the SWIR1 channel (1590–1675 nm) on the Sentinel 5 UVNS instrument can achieve <0.68 ppb. These uncertainties combined with modest spatial and/or temporal averaging techniques can reduce δ13C uncertainty to the target magnitude or better. However, we find that 13CH4 retrievals are highly sensitive to errors in a priori knowledge of temperature and pressure, and accurate knowledge of these profiles are required before 13CH4 retrievals can be performed on TROPOMI and future Sentinel 5/UVNS data.

“…Based on this limited spread of measurement sites, the existence of a satellite instrument that can differentiate between methane isotopologues would expand the global knowledge of methane distributions. It has been achieved in the upper troposphere and lower stratosphere with solar occultation limb viewing instruments (Buzan et al, 2016;Irion et al, 1996), and is hoped to be achieved with dedicated potential future instruments (Weidmann et al, 2017). The aim of this paper is to identify spectral regions where the main methane isotopologues ( 12 CH4 and 13 CH4) can be detected with the existing GOSAT Thermal and Near Infrared Sensor for carbon Observation Fourier Transform Spectrometer (GOSAT-TANSO-FTS).…”

Section: Introductionmentioning

confidence: 99%

A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

Müller

Walton

2019

Preprint

Measurements of methane isotopologues can differentiate between different source types, be they biogenic (e.g. marsh lands) or abiogenic (e.g. industry). Global measurements of these isotopologues would greatly benefit the current disconnect between top-down (knowledge from Chemistry Transport Models and satellite measurements) and bottom-up (in situ measurement inventories) methane measurements. However, current measurements of these isotopologues are limited to a small number of in situ studies and airborne studies. In this paper we investigate the potential for detecting the second most common isotopologue of methane ( 13 CH 4 ) from space using the Japanese Greenhouse Gases Observation Satellite (GOSAT) applying a quick and simple residual radiance analysis technique. The method allows for a rapid analysis of spectral regions, and can be used to teach University students or advanced school students about radiative transfer analysis. Using this method we find limited sensitivity to 13 CH 4 , with detections limited to total column methane enhancements of >6%, assuming a desert surface albedo of >0.3.