How to use FieldSpec to detect field spectral?
How to use FieldSpec to detect field spectral?
In remote sensing technology, it is very important to master the spectral radiation characteristics of various ground objects in order to accurately interpret multi-spectral images. The blog introduced the portable field spectradiometer mesure principle, working specification and precautions. The factors affecting spectral measurement are described briefy.
In the field of remote sensing, spectral instruments suitable for field measurement are needed in order to study the visible and near-infrared spectral bands of various ground objects or environments under natural conditions in the field. We used the Chinese company Optosky ATP9110 Broad Field Spectradiometer to measure the spectrum of ground objects in the field. The main technical indicators are as follows: wavelength range is 300-2500nm, spectral sampling interval is 0.4nm, SWIR is 2.0nm, wavelength accurary is ±0.5nm @ VIS; ±1.1nm @ SWIR.
ATP9110 Broad Field Spectradiometer can be used for the spectral radiation measurement of the visible near-infrared band of outdooer targets. The spectrometer can measure and obtain the spectral radiance of the ground object by using the solar radiation as the illumination source and the responsiveness calibration data. The reflectance reference plate. By measuring the calibrated diffuse reflectance reference plate, the total illumination of the ground and the spectral information of direct and diffuse illumination can be obtained. BRDF spectral information parameters of ground targets can be obtained by using a special auxiliary measuring mechanism.
In order to make the ground object spectral data reliable and high quality, and make the data easy to compare and apply, it is necessary to put forward the ground object spectral test specifications and measurement requirements.
Standard and Calibration:
The resolution width of 0.04-1.10um is less than 5nm, and 1.1-2.5um is less than 15nm. For ATP9110 field spectrometer, the initial wavelength was 314nm, the termination wavelength was 2514nm, and the wavelength step ltngth was 1nm, then the spectral resolution was 1nm@756nm/10nm@1400&2100nm.
The linear dynamic range has three orders of magnitude, the maximum signal corresponds to 0.8-1.0, and the white board illuminated by solar constant (<90%) has peak response output. Linear error less than 3% (regression error).
Calibration of spectral responsivity:
For targets with reflectivity less than or equal to 15% (greater than 1%), the SNR should be greater than 10. If the reflectivity is greater than 15%. SNR should be great than 20.
Field measurement methods and work specifications:
Objective to select:
The measured target should be representative and reflect the average naturalness of the measured target. The combined effect of target and background should be taken into account in the measurement of vegetation canopy and objects.
For areas without serious air pollution generally, tehe horizontal visibility during measurement is require to be no less than 10km.
Cloud cover is limited:
Solid angle of 90° around the sun, light cloud volume, no cirrus, cumulus, etc., light is stable.
Widnd power requirement:
During the measurement, the wind force was less than level 5; for the plants, the wind force was less than level 3.
Measurements were made from 11:30 a.m. to 14:30 a.m., before the spectral measurement of each ground object, calibration was performed on the alignment standard reference plate to obtain a baseline of nearly 100%, and the target feature was then measured. In order to compare the measured data with botained by the satellite sensor, the measuring instruments are measured vertically downward.
Attention of detection:
The basic requirement for field spectral testing is to be performed around noon on a sunny day with no more than level 5 wind. If the soil spectrum is tested, it must be performed after 3d rain.
In order to make the data representative, it is necessary to carefully compare and select the ground objects to be measured, and measure the same ground objects several times to ensure the accuracy and comparability of the test results.
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