The research in this thesis focuses on the ability of a proposed satellite mission, Traceable Radiometry Underpinning Terrestrial and Helio- Studies (TRUTHS), to detect signals of climate change as manifested in the Earth’s reflected shortwave spectrum.
TRUTHS aims to measure the total incoming solar irradiance, spectral solar irradiance
and Earth’s reflected shortwave radiation with sufficient radiometric accuracy to
enable rapid detection of signals of climate change above natural variability. Early
detection of such signals will potentially enable mitigation strategies to be employed
faster.
Initially, sensitivity studies were conducted to investigate the atmospheric and surface
variables that affect reflected shortwave spectra. TOA shortwave reflectances calculated from Climate Observation System Simulation Experiment (COSSE) data were then used to investigate how quickly changes could be detected above natural variability,
as manifested in the simulations, using a linear regression model. The shortest
detection times ranged from 7-15 years and 10-25 years under clear and all sky conditions
respectively. The impact of spatial resolution was investigated by comparing 10 degree
and 1.41 degree zonal average data. The 10 degree data provided 9.2% more detections at <20 years for all sky conditions than the high resolution data. The data were also separated into land and ocean to investigate the effect of surface type, however this in general yielded no clear improvement in detection times.
Finally, gaps were added to the data record to simulate realistic climate observation
scenarios. These gaps varied from 10 to 25 years, with records lengths of 3 or 5 years
based on the estimated lifetime of a TRUTHS mission. Detection times indicate that,
of the scenarios investigated, a repeating 5 year mission followed by a 10 year gap
is optimal, providing detection times of predominantly <20 years globally at 1600nm,
1680nm and 2190nm, and in the tropics at visible wavelengths.