Update November 5 at end of post
These charts come from the Arctic and Antarctic Research Institute, St. Petersburg, Russia. I downloaded the images from 2008 through 2017 without collusion from their publicly accessible website (here).
The brown blob in the middle is older ice surviving at least one summer’s melt, with the colors for first year and young ice shown in the enlarged legend above.
The 2007 chart is in a different format so appears separately. The 2007 coverage is limited on the North American side, but it does show how much of the Central Arctic multi-year ice was gone in 2007. The subsequent charts show recovery with a decline in 2012 (Great Arctic Cyclone year), followed by increases, especially this year.
As discussed in previous posts, the technology for remotely sensing ice thickness is immature, so multi-year ice serves as a proxy.
Update: Background in response to Caleb’s query
Caleb asked about Russian satellite data sources possibly substituting for US ones going out of service.
I found a 2009 presentation in English which answers most of this. Russian Space Infrastructure applied in the Arctic: sea ice application within Roshydromet by Vasily Smolyanitsky, Arctic and Antarctic Research Institute (AARI). Excerpts and images below. Read the full report to appreciate the scale of their efforts.
Coastal weather polar stations of Roshydromet make daily visual and instrumental ice observations on sea ice concentration and stages of ice development, ice thickness, forms of ice, ice drift and other phenomena. Icebreakers and icebreaking vessels on the NSR routes routinely (commonly once a day) report the main ice parameters describing ice navigation. Before 1994 aircraft ice reconnaissance flights were conducted in the Arctic usually on a monthly basis from November to April and on a 10-day internal during the summer navigation period.
Since 1995 aircraft (mostly helicopter) ice reconnaissance flights are conducted only occasionally during tailored hydrometeorological support of applied and scientific activities in the Eurasian Arctic. The scope of ice information collected during air ice reconnaissance includes visual observations on a full scope of sea ice parameters essential for navigation and marine safety (egg-code, icebergs, openings, dynamics, surface features). Though being nowadays not the prime sources, the stated information (coastal, aircraft) is continuously used for validation of the sea ice analysis and prognostic products at the ice centers.
The AARI and Planet satellite reception stations provide operational optical imagery for the Arctic Ocean and North Pacific from a series of satellites (NOAA, EOS TERRA, Aqua, Suomi NPP, FY3, Meteor, Ocean). Information for other regions (e.g. Antarctic), from other satellites and ranges (Sentinel-1,2,3, Radarsat-2, TerraSar-X, etc.) is received via Internet from corresponding data portals directly or from commercial satellite data providers. All data are further processed within ice information systems and utilized for regional, pan-Arctic or pan-Antarctic sea-ice analysis. Sample satellite products are available via the AARI and Planet web pages.
Most of the mentioned satellites are accessed by others with the exception of Meteor, operated by Russia. Yes, they have numerous meteorological satellites as shown in this image:
According to the presentation, their plans called for additional Electro and Meteor platforms, as well as a new satellite type called Arctica. It is not clear to what extent the sensors on these birds replicate the microwave data.