Passive microwave images of the polar regions, first produced after the launch of the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR)in December 1972, have become a valuable new source of polar information. Some of the potential applications of this new capability were anticipated. Of these, the sensing of sea ice through clouds and the polar night is probably the most important application for polar research and for operations on the polar seas. Other applications, such as the measurement of certain near-surfaceice sheet parameters, have been formulated more recently. Measurement of various ocean surface parameters is expected from the forthcoming multifrequency microwave observations. Undoubtedly additional uses of passive microwave datawill be conceived and developed. Two remarkable aspects of satellite-borne microwave radiometers are the complete spatial detail obtained by the scanning sensors and the temporal detail provided by continual coverage. For example, the observations of detailed microwave emission patterns over the Antarctic ice sheet should yield information that could not be obtained by surface or even aircraft measurements. Sequences of images produced at three-day intervalsreveal short-term ice sheet and sea ice phenomena that would otherwise be missed.

The English explorer Martin Frobisher rediscovered Greenland in 1578, during his third attempt to find a route north of America to the East Indies, and John Davis's subsequent expeditions in 1585-87 established contact with the Eskimos in Greenland. Christian IV, King of Denmark-Norway, fitted out three ships for Greenland in 1605 with the Englishman John Cunningham as commander and the Danish nobleman Godske Lindenow as second-incommand, but he lost interest when no valuable minerals were found. He did, however, reestablish the sovereignty of the Danish crown over Greenland, and thus laid the foundation for later colonization by Denmark.

Waders are among the most characteristic birds breeding in Arctic regions. The group includes species such as the Knot Calidris canutus and Turnstone Arenaria interpres whose breeding distribution spreads to the. most northerly points of land in the world, along the shores of Greenland and Ellesmere Island bordering the Arctic Ocean. To succeed, these species must be highly adapted to their environment, able to fit all the events of the nesting season—territorial procurement, laying, incubation and hatching of eggs, and raising of young—into the short Arctic summer, able to withstand extremes of weather and fluctuations in food supply, and to avoid the attentions of mammalian and avian predators. To exploit their Arctic niche, these birds make long and spectacular migrations from a wintering area where climate and food supply are suitable for subsistence but not for reproduction. Owing to the remoteness of the Arctic breeding areas, details of the migrations of these species have remained obscure or undocumented until relatively recently. This article describes the development of research on wader migration in Britain and the research expeditions which have taken place since 1970 to various Arctic, sub-Arctic (and sub-tropical) areas, and which together have clarified or solved many aspects of the migration of species wintering in Europe. Some of the features of the migration of the Knot are discussed in particular, as a representative species of the group.

In October 1976 HM nuclear submarine Sovereign was sent into the Arctic Ocean on a voyage to the North Pole. This was the second Royal Naval submarine deployment in the Arctic Ocean, the first being the voyage of the Dreadnought in 1971. Sovereign was accompanied by HM submarine Narwhal as far as 80°N, and within the Arctic Basin the submarine's track was flown over by a Canadian Argus maritime patrol aircraft. The Scott Polar Research Institute carried out a scientific programme from both vessels, with Dr P. Wadhams aboard Sovereign and V. A. Squire aboard Narwhal.

On 26 June 1976 a party of eight embarked MV Blenheim at Newcastle on the first stage of the expedition's journey to Svartisen. Situated on the Arctic Circle, north of the steel town of Mo-I-Rana, Svartisen is a plateau ice cap roughly 24 km in diameter. A deep valley, Glomdalen, running north-east to south-west splits the ice cap into two halves. Surveys made over the past 100 years have indicated that an extensive and almost continuous retreat of the ice limit has taken place.