Recent developments on low cost Unmanned Air Vehicles (UAVs) have opened new perspectives to environmental remote sensing. This work of thesis lead to the design and development of a lightweight and low-power instrumentation to remotely measure photosynthetic properties of terrestrial vegetation, through active sensing of fluorescence transients by means of UAVs. The instrument was designed to provide also 3D depth ranging information, exploiting direct TimeOf-Flight (dTOF) measurements, over a 50 m range with 2 cm resolution. Such depth information can be useful for both biomass measurements and UAV height control. The instrument is based on a smart pixel sensor including both a Single Photon Avalanche Diode (SPAD) and a Time-to-Digital Converter (TDC), a microcontroller and a dual-laser illuminator. One laser driver was properly designed to provide sub-nanosecond, 690 nm wavelenght laser pulses for dTOF measurements with up to 300 pJ per-pulse optical energy; the other one modulates a 405 nm wavelength laser to induce fluorescent transients. A coaxial optical system was conceived to excite the sample and to focus back the light signal onto the SPAD, including a main 8 mm lens, a 690 nm bandpass optical filter, and two laser diode collimators. In order to control the flow of operation of the sensor, display and save the pre-processed data, a graphical PC interface was also developed. After an in-depth characterization of system’s performance, the main functionalities of the sensor were tested, under di erent illumination conditions and at several distances of the specimen. Photosynthetic properties were collected by means of Laser-Induced Fluorescence Transient (LIFT) technique, at 4 m distance in just 5 ms dwell time. The depth ranging measurements instead demonstrate that a centimetre resolution can be obtained with moderate light background at a distance up to 10 m, range that can be extended up to 50 m by operating the sensor in dim light conditions.
Il recente sviluppo di veicoli aerei a controllo remoto (UAV) di basso costo ha aperto nuove prospettive per il telerilevamento ambientale. Durante questo lavoro di tesi è stato sviluppato uno strumento leggero e low power per misurare da un UAV le proprietà fotosintetiche della vegetazione terrestre. Con lo stesso strumento è anche possibile e ettuare misure dirette del tempo di volo (dTOF) entro un raggio di 50 m con 2 cm di risoluzione, al fine di fornire dati quantitativi sulla biomassa e sull’altezza del veicolo. Il sensore optoelettronico alla base dello strumento è uno smart-pixel basato su un Single Photon Avalanche Diode (SPAD) con un Time-to-Digital Converter (TDC) integrato. Il sistema include un microcontrollore e un illuminatore composto da due di erenti unità per il controllo di diodi laser. Una di queste è stata progettata come generatore di impulsi laser a 690 nm, di 300 pJ di durata inferiore al nanosecondo per misure dTOF; l’altra per modulare un laser a 405nm utilizzato per indurre transitori di fluorescenza. È stato inoltre sviluppato un sistema ottico coassiale, comprendente un obbiettivo principale da 8mm, un filtro ottico passabanda a 690 nm e due collimatori per diodi laser. Al fine di controllare il funzionamento del sensore, visualizzare e salvare i dati pre-elaborati, è stata sviluppata un’interfaccia grafica per PC. Dopo una dettagliata caratterizzazione delle performance del sistema, sono state testate le principali funzionalità del sensore in diverse condizioni di illuminazione e alle varie distanze. Misure di fluorescenza mostrano che il segnale LIFT può essere correttamente rilevato a 4 metri di distanza, in un tempo di acquisizione pari a 5 ms. Le proprietà fotosintetiche sono state rilevate tramite transitori di fluorescenze laser-indotti (LIFT) fino ad una distanza di 4 metri. Le misure di profondità dimostrano invece che può essere ottenuta una risoluzione del centimetro fino a 10 metri, mentre la massima distanza può essere estesa a 50 metri se il sensore viene operato in ambienti poco luminosi.
Low power instrument for vegetation inspection through single photon time of flight remote detection
MONTAGNANI, GIOVANNI LUDOVICO
2013/2014
Abstract
Recent developments on low cost Unmanned Air Vehicles (UAVs) have opened new perspectives to environmental remote sensing. This work of thesis lead to the design and development of a lightweight and low-power instrumentation to remotely measure photosynthetic properties of terrestrial vegetation, through active sensing of fluorescence transients by means of UAVs. The instrument was designed to provide also 3D depth ranging information, exploiting direct TimeOf-Flight (dTOF) measurements, over a 50 m range with 2 cm resolution. Such depth information can be useful for both biomass measurements and UAV height control. The instrument is based on a smart pixel sensor including both a Single Photon Avalanche Diode (SPAD) and a Time-to-Digital Converter (TDC), a microcontroller and a dual-laser illuminator. One laser driver was properly designed to provide sub-nanosecond, 690 nm wavelenght laser pulses for dTOF measurements with up to 300 pJ per-pulse optical energy; the other one modulates a 405 nm wavelength laser to induce fluorescent transients. A coaxial optical system was conceived to excite the sample and to focus back the light signal onto the SPAD, including a main 8 mm lens, a 690 nm bandpass optical filter, and two laser diode collimators. In order to control the flow of operation of the sensor, display and save the pre-processed data, a graphical PC interface was also developed. After an in-depth characterization of system’s performance, the main functionalities of the sensor were tested, under di erent illumination conditions and at several distances of the specimen. Photosynthetic properties were collected by means of Laser-Induced Fluorescence Transient (LIFT) technique, at 4 m distance in just 5 ms dwell time. The depth ranging measurements instead demonstrate that a centimetre resolution can be obtained with moderate light background at a distance up to 10 m, range that can be extended up to 50 m by operating the sensor in dim light conditions.| File | Dimensione | Formato | |
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2015_04_Montagnani.pdf
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https://hdl.handle.net/10589/106788