Difference of sea surface height and mean sea surface. Sea surface height may be corrected using models for effects such as tides and atmospheric forcing

Pertaining to the extent, depth, and longevity of snow pack.

Sentinel-1 is a constellation of two imaging radar satellites operated by ESA. Sentinel-1B experienced an anomaly which rendered it unable to deliver radar data in December 2021, and the launch of Sentinel-1C is planned for 2023.

Launched in October 2005, CryoSat was a next-generation radar altimetry mission, aiming to determine variations in the thickness of the Earth's continental ice sheets and marine ice cover. Primary objective is to test the prediction of thinning arctic ice due to global warming. CryoSat was supposed to be the first Earth Explorer Opportunity mission in ESA's Living Planet program, but was lost in a launch failure on 8 October 2005, prompting the development of a successor mission, CryoSat-2.

ClONO2 - This is a stratospheric reservoir species for chlorine and nitrogen, two of the catalysts in the breakdown of ozone. It reacts with HCl at low temperatures on the surfaces of polar stratospheric clouds (PSCs over Antarctica and possibly in the stratosphere over the Arctic). That normally slow reaction heterogeneously produces molecular chlorine and nitric acid. The former outgases from the PSC surface and is quickly photolyzed by 450 nm or shorter wavelength light to form chlorine radicals which rapidly catalyze the breakdown of ozone (see chlorine monoxide). [Science; v 238; pages 1258-1260; 1987.] [Science; v 258; pages 1342-1345; 1992.]

SARAL (Satellite with ARgos and ALtiKa) is an altimetric minisatellite operated by ISRO and CNES. Launched in 2013, data gathered by SARAL has applications in oceanography and atmospheric studies.

Sentinel-2 is a constellation of two optical imaging satellites, which are a part of Copernicus - the European Union's Earth observation program.

ICESat (Ice, Cloud, and Land Elevation Satellite) is a NASA/GSFC mission within the ESE (Earth Science Enterprise) program. The prime objective is to monitor the mass balance of the polar ice sheets and their contributions to global sea level change. Secondary goals are to measure cloud heights and the vertical structure of clouds and aerosols in the atmosphere, further to measure roughness, reflectivity, vegetation heights, snow-cover, and sea-ice surface characteristics, and to map topography of land surfaces. Note: ICESat is the renamed former "Laser Altimetry-1" mission.

The ERS-1 (European Remote Sensing Satellite -1) was the first environmental monitoring satellite developed by ESA. The mission detected land and ocean surface change and provided observation data on oceans, polar ice, vegetation, geology, meteorology and ecology.

ERS-2 (European Remote Sensing Satellite -2) was launched in April 1995, the ERS-2 was an enhancement of the previous ERS-1 mission. ERS-2 provided microwave spectrum environmental monitoring across a range of disciplines (oceans, polar ice, forestry).