Aimed at different understanding and view point,based on precise level monitoring,GPS techniques and systematic analysis of in situ monitoring data of scores of years,the authors put forward a perspective of surface subsidence has certain self recoverable capability,summed up the range of surface recoverable subsidence threshold,narrated rational method and in situ monitoring essentials.

In order to monitor land subsidence in Tianjin area,a GPS network was established in 1995 as a complementary means of the precise leveling.

The relative altitude variations at these points were analyzed using ten years replicated observations in this paper,and they were compared with the results of precise leveling by the authors.

On the basis of the research on the contrast between GPS and precise leveling from 1995 to 2004, the actual accuracy of the two methods is tested.

As a method of forest volume measurement, 3P sampling technology has been accepted in forestry field, but for the reason that two critical problems, precise monitoring of stand volume and fast generation of random data can t be solved well in traditional forestry resources monitoring, the technology has not been used widely for a long time.

It would expend more labor and material in the traditional precision leveling.