Remote sensing of greenhouse gases
Increasing concentrations of greenhouse gases are the main driver of global climate change, and these gases are most efficiently measured and monitored using satellites. We at the Atmospheric Remote Sensing group study both GOSAT and OCO-2 satellite measurements from different perspectives including algorithm development, uncertainty quantification and validation. One of our goals is to understand and quantify how scattering by aerosol and cloud particles affects the satellite retrievals. Another goal is to investigate spatiotemporal correlation structures through simulated observations. Our group also collaborates with FMI's Carbon Cycle Modelling group to estimate methane sources and sinks using the CarbonTracker inverse model system with GOSAT methane observations.

Carbon dioxide and methane concentrations are continuously measured at Sodankylä where FMI's Arctic Research Centre hosts a Fourier Transform Spectrometer that is part of the global TCCON network. Atmospheric Remote Sensing group studies the sensitivity of the retrieval to the prior profiles of these gases, and develops retrievals that use dimension reduction and Markov Chain Monte Carlo methods. In addition, we use the Sodankylä TCCON data for validation of GOSAT and OCO-2 satellite measurements at high latitudes.

Effects of Precipitating Energetic Particles in the Atmosphere
Energetic particle precipitation affects the neutral chemistry of the Earth's atmosphere in the polar regions. Energetic particles in this means either solar protons, cosmic rays or auroral electrons that are transported in the Earth's atmosphere by strong solar wind and/or big eruptions on the Sun's surface. As propagating in the Earth's atmosphere the energetic particles ionise atmospheric neutral molecules. As a result several ozone depleting substances, such as odd hydrogen and odd nitrogen, are being formed. Ozone is destroyed in catalytic chemical cycles in the middle and upper atmospheres with also long-term effects. Because ozone plays an important role in the heat balance of the atmosphere through UV absorption, changes in ozone balance affect also the dynamics of the atmosphere, possibly also the climate on Earth's surface. For more information, see the CHAMOS web pages.

Middle Atmosphere and Ozone
Ozone in the middle atmosphere is crucial for protecting biosphere from harmful UV-radiation. The dramatic loss of ozone in Antarctic (ozone hole), the similar but weaker loss of ozone in Arctic, and the general slow decline of ozone in the stratosphere have been the object of intensive experimental and modeling studies since 1985 when the ozone hole was first detected. The main processes behind ozone loss are already quite completely understood. There are some signs that the recovery of ozone has now started but the complete recovery is expected to take about fifty years. Ozone research in the Atmospheric Remote Sensing group is largely based on the use of data from three satellite instruments: GOMOS on Envisat, Osiris on Odin and OMI on EOS-Aura. Time series and climatologies of ozone and related nitrogen compounds (NO2 and NO3) have been calculated and compared to the ones from models. An important research direction is the interaction of the middle atmosphere ozone and NO2 with energetic particle precipitation from the Sun (for more information click here).

Stellar Scintillations for Mapping Turbulence and Gravity Waves
The upward propagating waves and their breaking into turbulence are of fundamental importance for the dynamics and mixing within the middle atmosphere.

The use of satellite observations of stellar scintillation for studying small-scale irregularities of the Earth atmosphere is a relatively new approach that allows quantification of the activity of small-vertical-scale gravity waves (GW) and their breaking into turbulence. After the launch of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite in March 2002, scintillation measurements became available with global coverage. The method for reconstruction of GW and turbulence spectra parameters from stellar scintillations has been recently developed and adapted to GOMOS measurements. GOMOS data have allowed obtaining information about spatiotemporal distributions of gravity wave and turbulence spectra parameters at altitudes 25-50 km. For more information click here.

Surface UV
The amount of solar UV radiation reaching the Earth's surface is mainly affected by the solar elevation and the atmospheric ozone absorption. Moreover, the surface albedo and the clouds and aerosols effect modulate the surface UV radiation levels. Changes in UV radiation at the surface may strongly affect human health and terrestrial and aquatic ecosystems. The UV Index, defined as the EDR (mW/m2) divided by 25, provides useful information for the public in order to prevent overexposure to the Sun's rays. Surface UV radiation estimates have been provided from satellite-based instruments such as OMI (Ozone Monitoring Instrument) and GOME-2 (Global Ozone Monitoring Experiment-2).The amount of surface UV radiation increased during the last 30 years because of the effect of the ozone decrease, combined with the effect of the cloud-aerosol reflectivity changes. These long-term changes can in general affect the global bio-geochemistry (carbon cycle), climate and their interactions. For more information see OMI UV web pages.

Method Development
The group has been active in developing computational, mathematical and statistical methods for remote sensing, especially those related to satellite retrieval. One special field of interest has been the development and application of Markov chain Monte Carlo (MCMC) simulation methodologies for uncertainty quantification in modelling. We are currently a partner in Academy of Finland's LASTU project NOVAC: Novel advanced mathematical and statistical methods for understanding climate and collaborate closely with the Finnish Centre of Excellence in Inverse Problems. Markov chain Monte Carlo (MCMC) simulation algorithms provide tools for carrying out Bayesian uncertainty quantification modelling. Advantage of these methods is that they are not restricted to linearizations or Gaussian approximations of the uncertainties; disadvantage being the added computational burden caused by the large number of forward model simulation required. We have been developing adaptive MCMC algorithms that allow for semi-automatic use of these methods even in high dimensional and computationally intensive problems. For more information, visit the MCMC toolbox for Matlab web page.

O3M SAF (Satellite Application Facilities)
Utilising specialist expertise from the Member States, Satellite Application Facilities (SAFs) are dedicated centres of excellence for processing satellite data and form an integral part of the distributed EUMETSAT Application Ground Segment. O3M SAF consortium members develop radiative transfer calculation methods and other algorithms for creating atmospheric remote sensing data from polar-orbiting satellite Metop-A. We also validate the data products and provide associated dissemination and user services. O3M SAF produces near real-time data products including total/tropospheric ozone and nitrogen dioxide, ozone profiles and clear-sky ultraviolet fields. Data is also archived for later access by researchers. This offline data includes surface ultraviolet fields, total and tropospheric ozone, ozone profiles, total amounts of chemically important trace gases such as nitrogen dioxide (NO₂), water vapour (H₂O), and bromine oxide (BrO) as well as stratospheric aerosols. For more information see O3M SAF web pages.

OMI VFD (Very Fast Delivery)
The OMI very fast delivery service offer near real time satellite measurements over the Northern Hemisphere. The measurements are from OMI (Ozone Monitoring Instrument) onboard the EOS-Aura satellite and the images and data come available within 15 minutes after the satellite overpass of Sodankylä Ground Station in Northern Finland. The data is received via Direct Broadcast transmission from the satellite at the same time with measurements. Thus, the service is faster than normal NRT delivery. The service provides latest observations of O₃, SO₂, clouds, UV index, UV daily dose and aerosols as individual and composite images. The applications are such as monitoring of UV index, ozone column and volcanic aerosols and SO₂. For more information see OMI VFD web pages.