Caracterização de um sistema imageador infravermelho termal através de suas resoluções espacial e radiométrica / Characterization of a thermal infrared line scanner trough its spatial and radiometric resolutions

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

The thermal infrared spectral bands in airborne sensors are still little explored in Brazil. The Institute of Advanced Studies (IEAv) at the Aerospace Technical Center (CTA) developed the Thermal Infrared Imaging System (SISIMI), an aerial surveillance prototype sensor operating in the 8 to 12.5 um band with a rotating imaging scanner of 720 lines/s. The objective of this dissertation is to characterize the SISIMI trough its spatial and radiometric resolutions. The Effective Instantaneous Field of View (EIFOV) was calculated with the Modulation Transfer Function (MTF), while the radiometric resolution was determined with the estimate of the Noise Equivalent Temperature Difference (NETD). The experiments were conducted at INPE?s Optical Sensors Laboratory and in the field with image acquisition flights. For the MTF determination in the laboratory, a collimator with slits was used to simulate the inpulse function and to obtain the output Point Spread Function (PSF). The PSF Fourier Transform determined the sensor MTF. In the NETD estimate, the SISIMI was placed at a bench to image three ontiguous recipients with clean water, thus simulating a black body. The peak-to-peak signal tension was measured by the application of a temperature difference between the target (central recipient) and the background (side recipients) and the "rms" noise tension was measured after the sealing of the optical aperture of the sensor,. The field MTF curve was obtained through the impulse function simulation in an airplane pass, when polished aluminum stripes were placed over a thick black plastic sheet, and the emissivity properties were also investigated. To obtain the NETD in the field, the plastic canvas became the target and the airfield concrete parking lot was the constant background. Based on the results found at three levels (theoretical, laboratory and field) an analysis of the consistency of the values obtained was made and the resolutions of the SISIMI prototype were determined: EIFOV = 12.6 ± 0.4 mrad, NETD = 1.2 ± 0.2 K. These values indicate limitations in the imager but are compatible with a prototype from the 80s?. Modifications are proposed in the sensor to improve the performance and quality of the images, such as an alignment of the optical system, reinforcement of the metallic shield of the prism?s motor and in the cabling that conducts the electric signals. The use of the SISIMI is suggested in military applications as well as in environmental research.

ASSUNTO(S)

signal to noise ratios point spread functions razão sinal modulation transfer function ruído função de transferência de modulação (ftm) imageadores infravermelho função de espalhamento pontual. key words: infrared scanners

ACESSO AO ARTIGO

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