11. Amirkhizi said he based his figures on ground surveys conducted by U . N . workers. 12. Despite a history of heart problems, he nevertheless conducted an on-ground survey of the fire site. 13. Ground surveys are performed by a mapper, on foot, bicycle, or in a car, motorcycle or boat.14. It was first roughly plotted from ground surveys and aerial photographs by the Byrd Antarctic Expedition, 1928-30. 15. It was mapped by United States Geological Survey ( USGS ) from ground surveys and Navy air photos. 16. The first work in 1977 was a ground survey and the 1980 investigation consisted of excavations on site. 17. Population trends have been measured through springtime Breeding Bird Surveys and, in the northern breeding range, springtime singing-ground surveys . 18. Because of the rugged terrain, the United Nations used not only helicopter overflights by technical experts but also ground surveys . 19. Burma's " forecast of opium production is based on actual ground surveys , whereas American surveys are based on satellite images. 20. Mapped by United States Geological Survey ( USGS ) from ground surveys and U . S . Navy air photos, 1959-71.
