What is field spectrometer?
, or geophysical spectrometer
, is a special instrument for resolving and capturing the intensity of specific wavelengths, providing special analytical services in various fields. The instrument can be used for the clinical identification of certain specific components in biological samples. Combined with the characteristics of nanotechnology, it can also provide technical assistance in the field of genetics.
The instrument can be used to measure the content of various substances in food samples, as well as for residue detection and nutritional analysis of food samples. Analysts can analyze the active ingredients of drugs and study the pharmacokinetics for drug development with the field spectrometer
The use of geophysical spectrometers
can reveal the production status, pesticide use status, and contamination status of specific agricultural products. Using modern technology, geophysical spectrometers can transform a large amount of data into a visual user interface that can help people to further study related problems.
The principle of geophysical spectrometry
is to use the high temperature of an electric arc to directly vaporize and excite the elements in the sample, emitting a specific wavelength for each element, which is then spectroscope by a grating to form a spectrum, arranged by wavelength. The characteristic spectral lines of such elements pass through the exit slit and are shot into the spectral lines of the respective photomultiplier tubes, which are then spectroscopically divided by the grating. The characteristic spectral lines are shot through the exit slit into the respective photomultiplier tube and the percentage of each element is printed.Geo-spectrometers
generally belong to atomic emission spectroscopy. It can be used in metallurgy, forging, non-ferrous metal identification, petrochemical, machinery manufacturing, and other industries.
Feature of field spectrometer
a. The characteristics of high automation, good selectivity, simple operation, and fast analysis of the field spectrometer
can be carried out simultaneously for multi-quantitative analysis. If more than 20 steel alloy elements are measured simultaneously in 1~2 minutes, the equipment can operate the melting process and speed up the steel-making process.
b. The high accuracy of the ground substance spectrometer is used for spectral analysis by the photoreceptor method. As the photographic plate and photometric error are generally above 1%, the error can be reduced to 0.2% when using the photoelectric method of measurement, so the accuracy is high, which is conducive to the analysis of high content elements in the sample.
c. The linear boundary width of the calibration curve. Considering the strong expansion effect of the broadcast TV multiplier tube on the flag, the spectral lines of different intensities can use the difference expansion multiplier (difference of 10,000 times), so it can measure many elements with large content differences in the sample under the unified analysis requirements.
d. The detection limit of the ground matter spectrometer is low, and the sensitivity placed by photoelectric spectral analysis is related to the nature of the light source, instrument form, test material composition, elemental nature, etc. In general, constant metals, alloys, or powders can be detected with a spark or arc light sources, and the detection limit can reach 0.1~10ug/g. The detection limit is 1ng/ml~1ug/ml when ICP samples are measured by ground substance spectrometer, and the vacuum photoelectric photometer has better detection limits for non-metals such as carbon, sulfur, and phosphorus.
How to choose a good field spectrometer?
A. The ability to test samples
The main role of the field spectrometer
is to perform accurate composition analysis of products, so good sample performance is the key to purchase. The broad-spectrum analyzer can better analyze the components, and the high sensitivity spectrophotometry is also more conducive to the determination of trace components in the sample, thus making the measurement results more accurate. In addition, the user can first try to understand the spectral range is more or less, the detection sensitivity is high or low, whether the operation is easy, whether the process requirements can achieve the desired results, and then decide whether to make the purchase.
B. Detection software system and operational stability
To achieve stable spectral scanning operation, the internal system and software of the instrument must be used in cooperation. Therefore, when choosing, attention should be paid to detecting and selecting a reliable software system to ensure that the spectrometer can adapt to different production and processing environments, and use its stable system to achieve operation. In a word, the stability of the field spectrometer must be good.
C. Formal channels of purchase
When selecting and purchasing, you must pay attention to whether it is a formal manufacturer, a formal agent, or a supplier. In the application process, expert guidance is needed to ensure the normal use of the instrument, especially after-sales service, including installation, commissioning, maintenance, upgrades, etc.
Use of field spectrometer
A. Instrument standards and calibrations
a. Spectral resolution
The practical resolution width is less than 5nm for 0.04~1.10μm and less than 15nm for 1.1~2.5μm. For a handheld portable field spectrometer, the starting wavelength is 325nm and the ending wavelength is 1075nm. If the wavelength step is 1nm, the spectral resolution is taken as 3nm.
b. Linear calibration
The linear dynamic range has 3 magnitudes, the maximum signal corresponds to 0.8 ~ 1.0, and the solar constant illumination of the whiteboard (<90%) peak response output. Linearity error is less than 3% (regression error).
c. Calibration of spectral responsivity
For targets with reflectance less than or equal to 15% (greater than 1%), the signal-to-noise ratio should be greater than 10. For targets with reflectance greater than 15%, the signal-to-noise ratio should be greater than 20.
B. Field measurement methods and work specifications
a. Target selection
The selection of measurement targets should be representative and should truly reflect the average naturalness of the measured targets. For the measurement of vegetation canopy and with objects, the combined effect of target and background should be considered.
b. Visibility requirements
In general, no serious air pollution areas, and the measurement of horizontal visibility requirements of not less than 10km.
c. Cloud amount limitation
90° stereo angle around the sun, light cumulus amount, no cirrus clouds, thick cumulus clouds, etc. Light is stable.
d. Wind force requirement
The wind is less than 5 levels during the measurement time, and for plants, the wind is less than 3 levels during the measurement.
e. Measurement method
Measurements should be performed from 11:30 to 14:30. Before each kind of feature spectral measurement, align the standard reference plate for calibration, get close to 100% baseline, then measure against the target feature; to make the measured data can be compared with the data obtained from the satellite sensor, the measuring instruments should all be measured vertically downward.
C. Notes on field spectral measurements
The basic requirement for field spectroscopy testing is to be conducted around noon on a sunny day with a wind force of no more than 5 degrees. If the soil spectrum is tested, it must be done after 3 days of rain.
To make the data representative, the measured features should be carefully compared and selected, and the same kind of features should be measured several times to ensure accurate and comparable test results.
a. Position of the instrument
The instrument is oriented downward to the measured object, keeping at least the angle normal to the horizontal plane within ±10° and maintaining a certain distance, with the probe height from the ground usually at 1.3m to obtain the average spectrum. The field of view can be calculated based on the relative height and field of view angle. If more than one probe is available, a wide field of view probe should be selected in the field as much as possible. When measuring plant canopy spectra, the most representative species should be selected for measurement.
b. Selection of sensor probes
When the range of field features is relatively large, species purity is relatively high, the observation distance is relatively close, the surveyor should choose a probe with a larger field of view. When the distribution area of features is small, species are mixed in the near distance or need to measure the distant features, then the surveyor should choose the probe with a small field of view.
c. Avoiding shadows
Shadows must be avoided when positioning the probe, and people should face the sunlight so that consistent measurement results can be obtained. When testing spectral data on a large scale in the field, measurement points need to be arranged along the opposite direction of shadows.
d. Whiteboard reflection calibration
A whiteboard calibration is required every few minutes in good weather to prevent drift in the sensor response system and the effects of changes in the sun's angle of incidence. If the weather is poor, calibration should be done more frequently. The whiteboard should be placed horizontally during calibration.
e. Prevention of light pollution
Do not wear light-colored, characteristic clothing and hats. If you wear white, bright red, yellow, green, and blue clothing and hats, it will change the reflective spectral characteristics of the reflected object.
Be careful to avoid their shadows falling on the target object. When using a dump truck or other platform to measure a ground object target from a height.
Be careful to avoid metal reflections, if any, you need to wrap the reflective parts with black cloth.
f. Observation time and frequency
Spectral testing should be done between 10:00 and 14:00 and under cloudless and clear skies, trying to avoid too early or too late. When time permits, try to measure as many spectra as possible. Test 5 data for each measurement point to get the average value and reduce noise and randomness.
g. Acquisition of auxiliary data
GPS data must be collected at all test sites, with detailed records of the location, vegetation cover, type, anomalous conditions of the measurement points, and the height of the probe. It is also paired with field photographic records to facilitate subsequent interpretation and analysis.
Field feature spectroscopy is a complex process that requires a combination of various spectral influences. The spectral data obtained by the surveyor is the result of various factors such as solar altitude angle, solar azimuth angle, clouds, wind, relative humidity, incidence angle, detection angle, instrument scanning speed, instrument field of view angle, instrument sampling interval, spectral resolution, slope direction, slope and spectral characteristics of the target itself. Before spectroscopic measurement, the surveyor should develop a corresponding test plan according to the measured target and task, exclude the influence of various interfering factors on the measured results, and make the obtained spectral data reflect the spectral characteristics of the target itself as much as possible, and record the parameters, instrument parameters and auxiliary information of the observed target (such as soil, vegetation, artificial target) in detail during the observation.Only in this way can the measured results be reliable and comparable, providing a basis for subsequent image interpretation and spectral reconstruction.
How to buy field spectrometer?
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