Remote Sensing Technology
Introduction
Remote Sensing Laboratory dedicates to the development of remote sensing instruments. It is the only team in Taiwan that deals with the remote sensing hardware. The laboratory has been established since 1997, and now has developed instruments as POS, micro-spectrometer, GISUAL, and VCDi.
POS
Panoramic Observation System (POS) consists with a 525 mm-focal-length Maksutov-Cassegrain telescope, a rotation stage and a PC controller. It is developed to demonstrate, on the ground, the performance of the self-made telescope whose original design concept is to be used in high altitude orbit. Performance tests have done on this telescope, while environmental tests have not. The focal plane of this telescope is a 4096 pixel CCD, and by rotating the stage, POS is able to capture panoramic images. One sample fused image scanned by POS is shown Fig. 1, in which the target distance is about 1.5 km, and commercial RGB filters are put in front of the focal plan.
Figure 1. RGB fused image of DanSuei area (red color of trees because of
NIR transmittance in red filter)
Micro-spectrometer
Micro-spectrometer is the payload of NSPO pico-satellite program, YAMSAT. To be adapted into the 10 × 10 × 10 cm3 size satellite, micro-spectrometer has a size of 8.5 × 7 × 1.5 cm3, weight of 57 grams, and power consumption of 450 mW. With spectral bands of 380 – 780 nm and resolution of 12 nm, micro-spectrometer aims to collect the solar spectrum and earth albedo information. Together with YAMSAT, it has been passed the radiation hardness, thermal cycle, vibration, and vacuum tests. YAMSAT is ready now, and expected to be launched at September 2003.
GISUAL
Ground-based Instrument for Sprites and Upper Atmospheric Lightning (GISUAL) is developed, according to the concept of science payload of ROCSAT-2, to monitor and record the phenomena of Sprites and upper atmospheric lighting. It contains 1 imager and 3 photometers of different spectral bands. One of the photometer serves as trigger source to controller and imager. The imager has capability to magnify dim signal to clear visible range, and it is designed specially for red sprite observation. Each photometer has one PMT to record the spectral and temporal signal of sprites. All information serves as research data for analyze the characteristics of sprites.
VCDi
Vegetation and Change Detection imager (VCDi) is a first self-made airborne multispectral imager in Taiwan. It has 4 spectral bands with IFOV 0.25 mini-radians and FOV 40°. Comprehensive function and performance tests have been carried out both in laboratory and outdoors. Collaborating with Agricultural and Forestry Aerial Survey Institute (AFASI), test flights on full modules have been successfully performed on 12 – 14 March, 2003. In order to measure the geometric accuracy of the system, targets and reflection plates have been placed in test area. The sample RGB and CIR images after radiometric and geometric calibration are shown as figure 2 and 3. One may see the back-and white reflection plates in the lower-right area in the images. The specification of VCDi is listed below:
| Item | Specification |
|---|---|
| IFOV | 0.25 mrad |
| FOV | ±14° × ±14° (transverse) ±20° (diagonal) |
| Effective focal length | 36 mm |
| Spectral ranges | B (450 – 520nm), G (530 – 610nm), R (630 – 690nm), NIR (780 – 900nm) |
| Radiometry accuracy | > 93% |
| System MTF | 0.15 (optical MTF:0.4) @ 56 lp/mm |
| System SNR | 20 @ 85 W/m2.sr.µm |
| Polarization sensitivity | < 3 % |
| Distortion | < 2 % |
| Stray light rejection ratio | < 2 % |
Figure 2. RGB image of test area
Figure 3. CIR image of test area
Internal teamwork makes us possible to design, manufacture, assemble, and test the instruments. The optical components, such as lenses, coating and filters, mainly come from internal optical shop and coating division, and mechanical parts from internal mechanical shop. It provides us a huge flexibility to design and assemble most desired instruments. Main efforts of the laboratory put on the system engineering. Working with the other organization, government funded, colleges or private corporations, the development of airborne and spaceborne remote sensing instruments continues.
