Company activities

Aʟᴏɴɢ-Tʀᴀᴄᴋ is mainly focused on the applications of remote sensing:

• Inland water surface monitoring from Altimetry and Imagery, where the first goal we constantly seek is to improve the vertical accuracy and precision of surface water height measurements from satellite as well as dealing with and improving the space-time resolution of the systems (to address smaller water bodies and shorter time scale hydrological events). In this objective, the company contributes to algorithms improvement from low level (stack filtering, waveform re-tracking, outlier rejections) to high level (river profiles, time-series, validation with fiducial, climatologies, global scale products). We also are automating as much as possible these tasks into and the quality control (validation and / or verification) of alti-hydro products.

• Sea Ice monitoring from Altimetry and Imagery, with the measurement of sea ice thickness from Altimetry, and the synergistic use of multiple imagery sensors data (optical, SAR) to derive sea ice maps that will help monitor the climate change and permit safe navigation near the poles. We are currently working on a SAR interferometric freeboard products and a SAR interferometric Swath product for sea ice, for an ESA funded project called Cryo-SEANICE.

• Aʟᴏɴɢ-Tʀᴀᴄᴋ S.A.S. develops SAR images segmentation tools to produce different types of masks such as inland water masks and sea ice masks to support altimetry data analysis, surface type verification and machine learning based approaches .

• Aʟᴏɴɢ-Tʀᴀᴄᴋ S.A.S. provides support and training to users of the Copernicus satellites data concerning hydrology, ocean and sea ice : Sentinel-1 (mainly) as well as Sentinel-2 and Sentinel-3 in the frame of the RUS Service (Research and User Support) https://rus-copernicus.eu/portal/.

Tools

Aʟᴏɴɢ-Tʀᴀᴄᴋ S.A.S. has developped a very comprehensive altimetry processing tool (AltiHydro) that is capable of processing the low level altimetry products (L1B) to high level outputs (L3 timeseries and L4 climatologies) and validating the water height measurement with fiducial data.

Aʟᴏɴɢ-Tʀᴀᴄᴋ S.A.S. has invested into dataservers that are dedicated to these tasks.

Context

Our planet is experiencing a faster climate change than initially expected. The impacts are many, among which the changes in continental surface water resources as well as ice and sea-ice extent at the poles. Aʟᴏɴɢ-Tʀᴀᴄᴋ is concerned with providing technology to monitor these changes, raise awareness and provide alerts thanks to satellite observing systems.

Surface Waters

Extreme events, such as droughts and floods, are forecast to increase as climate change takes hold.[143] Agriculture is among sectors most vulnerable to the impacts of climate change; water supply for example, will be critical to sustain agricultural production and provide the increase in food output required to sustain the world's growing population. In particular, fluctuations in the flow of rivers are likely to increase in the twenty-first century. Based on the experience of countries in the Nile river basin (Ethiopia, Kenya and Sudan) and other developing countries, depletion of water resources during seasons crucial for agriculture can lead to a decline in yield by up to 50% [144]. (1) Agriculture can both mitigate or worsen global warming. For example, in some places the extended duration of the dry season is worsen by new intensive agricultural practices that require more water than the traditional ones. As a consequence small reservoirs disapear and lakes are shrinking which requires more efforts to access water. According to a report by the International Water Management Institute and UNEP,[152] there is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. (1) As these issues occur over wide and sometimes trans-border geographical areas, it is hard for the authorities and humanitarian organizations to monitor the changes and to detect all of the critical situations. Satellite radar altimers and imagers offer night and day, all weather observing capabilities. They have the potential to regularly monitor the surface waters at regional and local scale. Nevertheless operational services are still missing. Mainly for two reasons : altimeters where initially designed to monitor oceans and scientist adapted the data processing techniques (retracking) from ocean to earth surfaces. The classical retracking techniques are not optimal for inlan waters (results are innacurate over small reservoirs and rivers). Thus the services cannot run in an automated way. For this reason only well gauged and well studied sites are addressed by the existing spacehydrology services. some technological locks are still to be broken to allow for automated processing and validation with insitu or cross-validation with long term validated series derived from previous altimeters.

Sea Ice thickness and extent

In the context of global warming new roads are opening up with less and thinner sea-ice, unfortunately making it possible to increase human activity such as shipping and the search for oil and gas. Nevertheless these roads are changing over time due to strong currents and need to be carefully monitored to avoid major hazards. Here again remote sensing satellites have a role to play. The remote sensing of sea-ice brings similar issues than those found on hydrology. The additional difficulty is that ground truth is is not easily at hand as the scene evolves quite fast (due to surface currents and atmospheric conditions). Repeated measurements are unlikely over few days. For these reasons, the existing services suffer either from poor validation, and/or low spatial resolution and/or small coverage.

(1) Credit & Acknowledgment to Wikipedia

Ongoing Works

Aʟᴏɴɢ-Tʀᴀᴄᴋ is bringing new ideas in to solve the aforementioned issues.

Sensing Continental Surface Water from Space

Aʟᴏɴɢ-Tʀᴀᴄᴋ is currently developping new retracking and new validation techniques on water height time series derived from radar altimeters onboard satellites. These will make it possible to extend the spatial coverage, the accuraty and the automation of existing and/or future spacehydrology services. Our retracking technology is the outcome of research activities that consider the following major observations such as :

Dominant echoes are often off-NADIR

Both over the inland water scenes and over sea-ice areas the dominant echoes mostly come from water surfaces, which may be off-nadir in contradiction to the homogeneous scene in the open ocean that favors the nadir direction. This was recently showned (Fig.A) by a member of our team [Bercher2013c] thanks to the ESA level-2 SARin mode Cryosat data.