HyperField, a constellation of polar sun-synchronous nanosatellites, is being developed by the
Finnish company Kuva Space. The constellation that will be launched in 2023 consists of 100
CubeSats with hyperspectral systems operating in the visible to near-infrared (VIS-NIR,
450-1100 nm) or Visible-to-shortwave infrared (VIS-SWIR, 450-2500 nm) ranges and provides
two to three times daily images of every location on Earth.
This paper presents the first and second generations of the Hyperfield satellites. It reviews along with their innovative platform and detector technology, the optical modes, planned mission operations, advanced AI-based processing architecture and novel algorithms are developed to improve the acquisition, enhance the image quality and produce tailored-based services.
Near Infrared (NIR) spectrometers have been widely used in many material inspection applications, but mainly in central laboratories. The role of miniaturization, robustness of spectrometer and portability are really crucial when field inspection tools should be developed. We present an advanced spectral sensor based on a tunable Microelectromechanical (MEMS) Fabry-Perot Interferometer which will meet these requirements. We describe the wireless device design, operation principle and easy-to-use algorithms to adapt the sensor to number of applications. Multiple devices can be operated simultaneously and seamlessly through cloud connectivity. We also present some practical NIR applications carried out with truly portable NIR device.
KEYWORDS: Sensors, Calibration, Microelectromechanical systems, Near infrared, Temperature metrology, Spectrometers, Control systems, Fabry–Perot interferometry, Monochromators, Data modeling
Near Infrared (NIR) spectrometers are widely used in many fields to measure material content, such as moisture, fat and
protein in grains, foodstuffs and pharmaceutical powders. These fields include applications where only highly
miniaturized and robust NIR sensors can be used due to small usable space, weight requirements and/or hostile working
environment. Handheld devices for material inspection, online process automation and automotive industry introduce
requirements for size, robustness and cost, which is currently difficult to meet. In this paper we present an advanced
spectral sensor based on a tunable Microelectromechanical (MEMS) Fabry-Perot Interferometer. The sensor is fibercoupled,
weighs 125 grams and fits to an envelope of 25x55x55 mm3. Three types of sensors cover the wavelength
ranges from 1.35-1.7 μm, 1.55-2.0 μm and 1.7-2.2 μm, utilizing only a single pixel extended InGaAs detector, avoiding
the expensive linear array detectors. We describe the design, principle of operation and calibration methods together with
the control schemes. Some environmental tests are described and their results and finally application measurement
results are presented along with discussion and conclusions.
Standoff Raman imaging systems have shown the ability to detect single explosives particles. However, in many cases, the laser intensities needed restrict the applications where they can be safely used. A new generation imaging Raman system has been developed based on a 355 nm UV laser that, in addition to eye safety, allows discrete and invisible measurements. Non-dangerous exposure levels for the eye are several orders of magnitude higher in UVA than in the visible range that previously has been used. The UV Raman system has been built based on an UV Fabry-Perot Interferometer (UV-FPI) developed by VTT. The design allows for precise selection of Raman shifts in combination with high out-of-band blocking. The stable operation of the UV-FPI module under varying environmental conditions is arranged by controlling the temperature of the module and using a closed loop control of the FPI air gap based on capacitive measurement. The system presented consists of a 3rd harmonics Nd:YAG laser with 1.5 W average output at 1000 Hz, a 200 mm Schmidt-Cassegrain telescope, UV-FPI filter and an ICCD camera for signal gating and detection. The design principal leads to a Raman spectrum in each image pixel. The system is designed for field use and easy manoeuvring. Preliminary results show that in measurements of <60 s on 10 m distance, single AN particles of <300 μm diameter can be identified.
VTT has developed Fabry-Pérot Interferometers (FPI) for visible and infrared wavelengths since 90’s. Here we present
two new platforms for mid-infrared gas spectroscopy having a large optical aperture to provide high optical throughput
but still enabling miniaturized instrument size. First platform is a tunable filter that replaces a traditional filter wheel,
which operates between wavelengths of 4-5 um. Second platform is for correlation spectroscopy where the
interferometer provides a comb-like transmission pattern mimicking absorption of diatomic molecules at the wavelength
range of 4.7-4.8 um. The Bragg mirrors have 2-4 thin layers of polysilicon and silicon oxide.
VTT Technical research centre of Finland has developed a MEMS Fabry-Perot interferometer (FPI) for the wavelength range from 7.5 μm to 9.5 μm. The device consists of two Distributed Bragg Reflectors (DBR) manufactured with MEMS processing techniques. The full width half maximum of the transmission peak is 150nm. This transmission peak can be tuned from 7.5 μm to 9.5 μm by applying a control voltage from 0 V to 30 V. A laboratory demonstrator has been put together to show the use of this module as a part of a spectral measurement setup. Several gas samples have been measured with the setup and compared against measurement results found in literature.
VTT Technical Research Centre of Finland has developed Tunable Fabry-Perot Interferometer (FPI) based miniaturized
hyperspectral imager which can be operated from light weight Unmanned Aerial Vehicles (UAV). The concept of the
hyperspectral imager has been published in the SPIE Proc. 7474, 8174 and 8374. This instrument requires dedicated
laboratory and on-board calibration procedures which are described. During summer 2012 extensive UAV
Hyperspectral imaging campaigns in the wavelength range 400 - 900 nm at resolution range 10 - 40 nm @ FWHM were
performed to study forest inventory, crop biomass and nitrogen distributions and environmental status of natural water
applications. The instrument includes spectral band limiting filters which can be used for the on-board wavelength scale
calibration by scanning the FPI pass band center wavelength through the low and high edge of the operational
wavelength band. The procedure and results of the calibration tests will be presented. A short summary of the performed
extensive UAV imaging campaign during summer 2012 will be presented.
Different remote sensing methods for detecting variations in agricultural fields have been studied in last two decades.
There are already existing systems for planning and applying e.g. nitrogen fertilizers to the cereal crop fields. However,
there are disadvantages such as high costs, adaptability, reliability, resolution aspects and final products dissemination.
With an unmanned aerial vehicle (UAV) based airborne methods, data collection can be performed cost-efficiently with
desired spatial and temporal resolutions, below clouds and under diverse weather conditions. A new Fabry-Perot
interferometer based hyperspectral imaging technology implemented in an UAV has been introduced. In this research,
we studied the possibilities of exploiting classified raster maps from hyperspectral data to produce a work task for a
precision fertilizer application. The UAV flight campaign was performed in a wheat test field in Finland in the summer
of 2012. Based on the campaign, we have classified raster maps estimating the biomass and nitrogen contents at
approximately stage 34 in the Zadoks scale. We combined the classified maps with farm history data such as previous
yield maps. Then we generalized the combined results and transformed it to a vectorized zonal task map suitable for farm
machinery. We present the selected weights for each dataset in the processing chain and the resultant variable rate
application (VRA) task. The additional fertilization according to the generated task was shown to be beneficial for the
amount of yield. However, our study is indicating that there are still many uncertainties within the process chain.
VTT Technical Research Centre of Finland has developed microelectromechanical (MEMS) Fabry-Perot interferometer (FPI) for hydrocarbon measurements. Fabry-Perot interferometer is a structure where is two highly reflective surfaces separated by a tunable air gap. The MEMS FPI is a monolithic device, i.e. it is made entirely on one substrate in a batch process, without assembling separate pieces together. The gap is adjusted by moving the upper mirror with electrostatic force, so there are no actual moving parts. The manufactured MEMS FPIs have been characterized. The tuning wavelength range of the MEMS FPI is 2.8-3.5 μm and its spectral resolution is 50-60 nm. VTT has designed and manufactured a handheld size demonstrator device based on the technology presented in this abstract. This device demonstrates gas detecting by measuring cigarette lighter gas and various plastic materials transmission spectra. The demonstrator contains light source, gas cell, MEMS FPI, detector and control electronics. It is connected to a laptop by USB connection, additional power supply or connection is not needed.
VTT Technical Research Centre of Finland has developed a Fabry-Perot Interferometer (FPI) based hyperspectral imager
compatible with light weight UAV (Unmanned Aerial Vehicle) platforms (SPIE Proc. 74741, 8186B2). The FPI based
hyperspectral imager was used in a UAV imaging campaign for forest and agriculture tests during the summer 2011
(SPIE Proc. 81743). During these tests high spatial resolution Color-Infrared (CIR) images and hyperspectral images
were recorded on separate flights. The spectral bands of the CIR camera were 500 - 580 nm for the green band,
580 - 700 nm for the red band and 700 - 1000 nm for the near infrared band. For the summer 2012 flight campaign a new
hyperspectral imager is currently being developed. A custom made CIR camera will also be used. The system which
includes both the high spatial resolution Color-Infrared camera and a light weight hyperspectral imager can provide all
necessary data with just one UAV flight over the target area. The new UAV imaging system contains a 4 Megapixel CIR
camera which is used for the generation of the digital surface models and CIR mosaics. The hyperspectral data can be
recorded in the wavelength range 500 - 900 nm at a resolution of 10 - 30 nm at FWHM. The resolution can be selected
from approximate values of 10, 15, 20 or 30 nm at FWHM.
VTT Technical Research Centre of Finland has developed a Fabry-Perot Interferometer (FPI) based hyperspectral imager
compatible with the light weight UAV platforms. The concept of the hyperspectral imager has been published in the
SPIE Proc. 7474 and 7668. In forest and agriculture applications the recording of multispectral images at a few
wavelength bands is in most cases adequate. The possibility to calculate a digital elevation model of the forest area and
crop fields provides means to estimate the biomass and perform forest inventory. The full UAS multispectral
imaging system will consist of a high resolution false color imager and a FPI based hyperspectral imager which can be
used at resolutions from VGA (480 x 640 pixels) up to 5 Mpix at wavelength range 500 - 900 nm at user selectable
spectral resolutions in the range 10...40 nm @ FWHM. The resolution is determined by the order at which the Fabry-
Perot interferometer is used. The overlap between successive images of the false color camera is 70...80% which makes
it possible to calculate the digital elevation model of the target area. The field of view of the false color camera is
typically 80 degrees and the ground pixel size at 150 m flying altitude is around 5 cm. The field of view of the
hyperspectral imager is presently is 26 x 36 degrees and ground pixel size at 150 m flying altitude is around 3.5 cm. The
UAS system has been tried in summer 2011 in Southern Finland for the forest and agricultural areas. During the first test
campaigns the false color camera and hyperspectral imager were flown over the target areas at separate flights. The design and calibration of the hyperspectral imager will be shortly explained. The test flight campaigns on forest and crop fields and their preliminary results are also presented in this paper.
VTT Technical Research Centre of Finland has developed a lightweight Fabry-Perot interferometer based hyperspectral
imager weighting only 400 g which makes it compatible with various small UAV platforms. The concept of the
hyperspectral imager has been published in SPIE Proc. 74741 and 76682. This UAV spectral imager is capable of
recording 5 Mpix multispectral data in the wavelength range of 500 - 900 nm at resolutions of 10-40 nm,
Full-Width-Half-Maximum (FWHM). An internal memory buffer allows 16 Mpix of image data to be stored during one
image burst. The user can configure the system to take either three 5 Mpix images or up to 54 VGA resolution images
with each triggering. Each image contains data from one, two or three wavelength bands which can be separated during
post processing. This allows a maximum of 9 spectral bands to be stored in high spatial resolution mode or up to 162
spectral bands in VGA-mode during each image burst. Image data is stored in a compact flash memory card which
provides the mass storage for the imager. The field of view of the system is 26° × 36° and the ground pixel size at 150 m
flying altitude is around 40 mm in high-resolution mode. The design, calibration and test flight results will be presented.
Miniaturized spectrometers covering spectral regions from UV to thermal IR are of interest for several applications. For
these purposes VTT has for many years been developing tuneable MEMS-based and more recently piezo-actuated
Fabry-Perot Interferometers (FPIs). Lately several inventions have been made to enter new wavelengths in the VIS range
and enlarge apertures of MEMS devices and also extending the wavelength range of piezo-actuated FPIs. In this paper
the background and the latest FPI technologies at VTT are reviewed and new results on components and system level
demonstrators are presented. The two FPI technologies are compared from performance and application point of view.
Finally insight is given to the further development of next generation devices.
VTT Technical Research Centre of Finland has developed a new low cost hand-held staring hyperspectral imager for
applications previously blocked by high cost of the instrumentation. The system is compatible with standard video and
microscope lenses. The instrument can record 2D spatial images at several wavelength bands simultaneously. The
concept of the hyperspectral imager has been published in SPIE Proc. 7474. The prototype fits in an envelope of 100
mm x 60 mm x 40 mm and its weight is ca. 300 g. The benefits of the new device compared to Acousto-Optic Tunable
filter (AOTF) or Liquid Crystal Tunable Filter (LCTF) devices are small size and weight, speed of wavelength tuning,
high optical throughput, independence of polarization state of incoming light and capability to record three wavelengths
simultaneously. The operational wavelength range with Silicon-based CCD or CMOS sensors is 200 - 1100 nm and
spectral resolution is 2 - 10 nm @ FWHM. Similar IR imagers can be built using InGaAs, InSb or MCT imaging
sensors. The spatial resolution of the prototype is 480 x 750 pixels. It contains control system and memory for the image
data acquisition. It operates either autonomously recording hyperspectral data cubes continuously or controlled by a
laptop computer. The prototype was configured as a hyperspectral microscope for the spectral range 400 - 700 nm. The
design of the hyperspectral imager, characterization results and sample measurement results are presented.
KEYWORDS: Imaging systems, Hyperspectral imaging, Image sensors, Fabry–Perot interferometry, Spectral resolution, RGB color model, Unmanned aerial vehicles, Linear filtering, Data conversion, Control systems
VTT Technical Research Centre of Finland has developed a new miniaturized staring hyperspectral imager with a weight
of 350 g making the system compatible with lightweight UAS platforms. The instrument is able to record 2D spatial
images at the selected wavelength bands simultaneously. The concept of the hyperspectral imager has been published in
the SPIE Proc. 74741. The operational wavelength range of the imager can be tuned in the range 400 - 1100 nm and
spectral resolution is in the range 5 - 10 nm @ FWHM. Presently the spatial resolution is 480 × 750 pixels but it can be
increased simply by changing the image sensor. The field of view of the system is 20 × 30 degrees and ground pixel size
at 100 m flying altitude is around 7.5 cm. The system contains batteries, image acquisition control system and memory
for the image data. It can operate autonomously recording hyperspectral data cubes continuously or controlled by the
autopilot system of the UAS. The new hyperspectral imager prototype was first tried in co-operation with the Flemish
Institute for Technological Research (VITO) on their UAS helicopter. The instrument was configured for the spectral
range 500 - 900 nm selected for the vegetation and natural water monitoring applications. The design of the UAS
hyperspectral imager and its characterization results together with the analysis of the spectral data from first test flights
will be presented.
In many hyperspectral applications it is beneficial to produce 2D spatial images with a single exposure at a few selected
wavelength bands instead of 1D spatial and all spectral band images like in push-broom instruments. VTT has developed
a new concept based on the Piezo actuated Fabry-Perot Interferometer to enable recording of 2D spatial images at the
selected wavelength bands simultaneously. The sensor size is compatible with light weight UAV platforms. In our
spectrometer the multiple orders of the Fabry-Perot Interferometer are used at the same time matched to the sensitivities
of a multispectral RGB-type image sensor channels.
We have built prototypes of the new spectrograph fitting inside of a 40 mm x 40 mm x 20 mm envelope and with a mass
less than 50 g. The operational wavelength range of built prototypes can be tuned in the range 400 - 1100 nm and the
spectral resolution is in the range 5 - 10 nm @ FWHM. Presently the spatial resolution is 480 x 750 pixels but it can be
increased simply by changing the image sensor. The hyperspectral imager records simultaneously a 2D image of the
scenery at three narrow wavelength bands determined by the selected three orders of the Fabry-Perot Interferometer
which depend on the air gap between the mirrors of the Fabry-Perot Cavity. The new sensor can be applied on UAV,
aircraft, and other platforms requiring small volume, mass and power consumption. The new low cost hyperspectral
imager can be used also in many industrial and medical applications.
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