Satellite Validation (SV)

Principal Participants: Walker, Drummond, Duck, Sica, Strong, Hocking, Manney; Canadian Gov't Departments: EC, CSA; International Orgs: NASA, ESA, JAXA; HQP: PDF + 2 graduate students.

Rationale Satellite data are integral to Arctic research and monitoring programs, as they provide a global context to the measurements made at ground-based observatories such as PEARL. To make the best use of these satellite measurements, it is essential to have properly validated data available.
Satellite validation is the process of establishing the accuracy and reliability of satellite measurements through comparisons with well-characterized data sets such as those produced from PEARL. It is an activity that must be continued throughout the life of a satellite mission to ensure the on-going data quality. It is not sufficient to undertake validation activities in the first year or two of a mission and assume that results will be identical for all subsequent years. While most satellite instruments are designed to operate for two or five years, many are able to extend their operations well beyond this to lifetimes of 10, 15 or more years. At present, there is a strong international focus on creating extended, multi-satellite time series, including ECVs, to monitor ozone recovery and other climate-related atmospheric changes. The stability of long-term satellite data sets is impacted by changes in satellite or instrument performance that can result from environmental degradation over these extended operating periods. By conducting on-going validation, we ensure that these satellite data sets are trusted and well-understood for use in long-term data studies and international assessments. In addition, new products and data versions are developed throughout each mission. These updates and new datasets must be evaluated and validated before being used widely in the scientific community. For these satellite validation activities, there is a need for well-characterized, multi-year and continuing datasets and the HQP trained in performing these assessments.

PEARL is a highly desirable site for satellite validation, being in a “sweet-spot” for satellite overpasses – 80N is the latitude for the most frequent overpasses by many polar-orbiting satellites – and located in the High Arctic where there are very few validation measurements available. Most of the measurements undertaken in the previous two themes will be included in this validation work. For example, PEARL is virtually unique in terms of its potential for polar night validation of satellite retrievals (e.g., from the CALIPSO lidar, the CloudSat radar and the CALIPSO IR imager). The suite of trace gases measured at PEARL is invaluable for the validation of Arctic measurements made by instruments on missions such as ACE, Odin/OSIRIS, Aura, MetOp and OMPS. The greenhouse gas measurements will be used to validate the GOSAT and OCO-2 missions. Working with the different satellite instrument teams, we have utilized PEARL data (taken between 2005 and 2012) to validate measurements by the Canadian ACE and Odin instruments, the NASA Cloudsat radar and the Japanese GOSAT satellite (~15 validation papers have been produced to date using PEARL data). The scientific teams associated with these sensors are keenly interested in the validation resources that PEARL offers and in continuing existing and establishing new partnerships.

In addition to providing validation for the current atmospheric observation satellites and their data products, new data needs are being identified for upcoming and planned missions. Future launches include ESA's ADM-Aeolus wind lidar for which the wind profiler radar provides validation. In the area of trace gas measurements, the FTIR and UV-Vis spectrometers provide comparison results for the Sentinel-5 precursor and next two MetOp satellites. Later in the decade, Canada's PCW satellite is anticipated. Although the launch does not overlap with the period of this application, preparation for measurements by providing pre-launch data and setting up the parameters for a validation effort are significant activities. Water vapour, already discussed under both the CM and PN Themes, is of particular interest in this context. Working with the international validation community through the Committee on Earth Observation Satellites, we will ensure that the PEARL measurements are included in future validation programs. It is essential to process the data to produce high precision and accuracy products and to ensure that they are inserted into global databases of validation measurements (including the NDACC, TCCON, and AERONET databases mentioned above).