Sampling survey to the total area of the forest of Heshun county in Shanxi province in year 2000
Implementation steps:
- Calculate the total optimal sample size n according to the known accuracy requirement;
- Calculate the sample size nh of each layer h according to the proportion distribution and optimal distribution design of the sample size;
- Extract nh samples from the layer h respectively according to the simple random sampling method;
- Estimate the population mean according to the mean of the sampling sites, then the mean multiply 2,697,460, the result is the estimated total area (unit m2）, and estimate the sampling accuracy.
Sample size according to the optimal distribution design:
- Total optimal sample size:
- Sample size of each layer:
- The total forest area is estimated according to the mean of 87 pixels:
The total optimal sample size is 78 in fact
The sampling size after extending 10% is 87
Sampling accuracy :
；
Popolation size 
of each layer; ；
Each layer variance 
；
Each layer cost 
；
Layer mean 
；
Layer weight 
；
Population mean 
；
Variance