Physicist uses satellite imagery to measure climate change

Rehan Siddiqui's research is grounded in the captivating field of remote sensing, but in space - using different types of atmospheric profiles of greenhouse gasses. This provides more insight into the mechanism of clouds - or cloud scenes - and how they navigate different layers in the atmosphere.

photo of Rehan Siddiqui

Rehan Siddiqui

His current task aims to determine the efficient detection of clouds scenes with the percentage of greenhouse gases, specially water vapour, carbon dioxide and methane, and its effects on the surrounding climate. The application of cloud scenes and climate effects of the Earth’s surface is still an ongoing debate in the scientific community.

"Satellite-based measurement of atmospheric absorption spectra in the near-infrared (NIR) band is a powerful tool for monitoring greenhouse-gases and other pollutants," Rehan says.

"In addition to extracting information about concentrations of specific constituents, absorption spectra can also be used to detect the presence of cloud layers, which alter the spectral radiance profile due to their enhanced reflectivity."

Knowledge of cloud characteristics is important for weather and climate studies. The presence of clouds can alter the energy budget of the Earth atmosphere system through scattering and absorption of shortwave radiation and the absorption and reemission of infrared radiation at longer wavelengths.

photo of the Argus atmospheric spectrometer

Argus atmospheric spectrometer

The instrument used measure atmospheric absorption, Argus, also has a connection to York University. Argus was developed at York and in association with Thoth Technology Inc. The instrument operates in the infrared, observing the radiation leaving the Earth's surface and atmosphere. In the infrared spectrum, absorption by water, clouds and carbon dioxide trap the sun's energy near the surface keeping the planet hospitable for life. Increased industrialization and greenhouse gas utilization is modifying the radiation environment changing the pattern that Earth's absorbs sunlight leading to climate change.

Argus has the capability to observe the radiation effect caused by surface pollution plumes. With a spatial accuracy of 1.5km Argus can observe directly large emissions of carbon-dioxide a primary greenhouse gas.

Rehan says, analysis of absorption spectra begins with a calibrated set of satellite-based measurements, taken with the Argus spectrometer on a specific trajectory over Earth’s surface. These data are compared to GENSPECT, a line-by-line radiative-transfer algorithm that models a reference atmosphere and computes a path-based absorption profile for a number of important gases. The relative concentrations of gases can be varied, along with other model parameters, until a good match to the measured spectrum is achieved, usually over an absorption-band specific to the molecule of interest.

The main reason he came to York, Rehan says, "was to work with my supervisor Dr. Brendan Quine. His research work closing matches with my thoughts and different atmospheric mysteries, and he spends most of his time with a lot of exciting and innovative work in space industry and related sectors. His specialist capabilities include spacecraft system development and the certification and test of space equipment’s. He is principal investigator for the Space Elevator, Northern Light mission to Mars and the mini spectrometer Argus 1000, a pollution monitor."

Additionally, "He is a great advisor, teacher and very enjoyable to work with," Rehan says. "I look forward to continuing our research and doing some great work with him."

Working with such high calibre researchers, such as those he's found here at York, will not only elevate his degree, Rehan says, "but will also help me to stay on top of the physics and space science industry. I believe that with my capacity for diligence, commendable logic and commitment to achieve my goals, I will be able to do very well in this field. This new approach will be added to weather research and forecasting data assimilation system."