title: Investigation of jitter on full-field amplitude modulated continuous wave time-of-flight range imaging cameras

authors: Anthonys, Gehan

subjects: jitter

abstract: The time-of-flight (ToF) range imaging cameras indirectly measure the time taken from the modulation light source to the scene and back to the camera and it is this principle that is used in depth cameras to perform depth measurements. This thesis is focused on ToF cameras that are based on the amplitude modulated continuous wave (AMCW) lidar techniques which measure the phase difference between the emitted and reflected light signals. Due to their portable size, feasible design, low weight and low energy consumption, these cameras have high demand in many applications. Commercially available AMCW ToF cameras have relatively high noise levels due to electronic sources such as shot noise, reset noise, amplifier noise, crosstalk, analogue to digital converters quantization and multipath light interference. Many noise sources in these cameras such as harmonic contamination, non-linearity, multipath interferences and light scattering are well investigated. In contrast, the effect of electronic jitter as a noise source in ranging cameras is barely studied.

Jitter is defined to be any timing movement with reference to an ideal signal. An investigation of the effect of jitter on range imaging is important because timing errors potentially could cause errors in measuring phase, thus in range. The purpose of this research is to investigate the effect of jitter on range measurement in AMCW ToF range imaging. This is achieved by three main contributions: a development of a common algorithm for measurement of the jitter present in signals from depth cameras, secondly the proposal of a cost effective alternative method to measure jitter by using a software defined radio receiver, and finally an analysis of the influence of jitter on range measurement. 

Among the three contributions of this thesis, first, an algorithm for jitter extraction of a signal without access to a reference clock signal is proposed. The proposed algorithm is based upon Fourier analysis with signal processing techniques and it can be used for real time jitter extraction on a modulated signal with any kind of shape (sinusoidal, triangular, rectangular). The method is used to measure the amount of jitter in the light signals of two AMCW ToF range imaging cameras, namely, MESA Imaging SwissRanger 4000 and SoftKinetic DepthSense 325. Periodic and random jitter were found to be present in the light sources of both cameras with the MESA camera notably worse with random jitter of (159.6 +/- 0.1) ps RMS in amplitude.

Next, in a novel approach, an inexpensive software defined radio (SDR) USB dongle is used with the proposed algorithm to extract the jitter in the light signal of the above two ToF cameras. This is a cost effective alternative to the expensive real-time medium speed digital oscilloscope. However, it is shown that this method has some significant limitations, (1) it can measure the jitter only up to half of the intermediate-frequency obtained from the down shift of the amplified radio frequency with the local oscillator which is less than the Nyquist frequency of the dongle and (2) if the number of samples per cycle captured from this dongle is not sufficient then the jitter extraction  does not succeed since the signal is not properly (smoothly) represented.

Finally, the periodic and random jitter influence on range measurements made with AMCW range imaging cameras are studied. An analytical model for the periodic jitter on the range measurements under the heterodyne and homodyne operations in AMCW ToF range imaging cameras is obtained in the frequency domain. The analytical model is tested through simulated data with various parameters in the system. The product of angular modulation frequency of the camera and the amplitude of the periodic jitter is a characteristic parameter for the phase error due to the presence of periodic jitter. We found that for currently available AMCW cameras (modulation frequency less than 100 MHz), neither periodic nor random jitter has a measurable effect on range measurement. But with modulation frequency increases and integration period decreases likely in the near future, periodic jitter may have a measurable detection affect on ranging.

The influence of random jitter is also investigated by obtaining an analytical model based on stochastic calculus by using fundamental statistics and Fourier analysis. It is assumed that the random jitter  follows the Gaussian distribution. Monte Carlo simulation is performed on the model obtained for a 1 ms integration period. We found increasing the modulation frequency above approximately 400 MHz with random jitter of 140 ps has a measurable affect on ranging.

text: Investigation of jitter on full-field amplitude modulated continuous wave time-of-flight range imaging cameras The time-of-flight (ToF) range imaging cameras indirectly measure the time taken from the modulation light source to the scene and back to the camera and it is this principle that is used in depth cameras to perform depth measurements. This thesis is focused on ToF cameras that are based on the amplitude modulated continuous wave (AMCW) lidar techniques which measure the phase difference between the emitted and reflected light signals. Due to their portable size, feasible design, low weight and low energy consumption, these cameras have high demand in many applications. Commercially available AMCW ToF cameras have relatively high noise levels due to electronic sources such as shot noise, reset noise, amplifier noise, crosstalk, analogue to digital converters quantization and multipath light interference. Many noise sources in these cameras such as harmonic contamination, non-linearity, multipath interferences and light scattering are well investigated. In contrast, the effect of electronic jitter as a noise source in ranging cameras is barely studied.

Jitter is defined to be any timing movement with reference to an ideal signal. An investigation of the effect of jitter on range imaging is important because timing errors potentially could cause errors in measuring phase, thus in range. The purpose of this research is to investigate the effect of jitter on range measurement in AMCW ToF range imaging. This is achieved by three main contributions: a development of a common algorithm for measurement of the jitter present in signals from depth cameras, secondly the proposal of a cost effective alternative method to measure jitter by using a software defined radio receiver, and finally an analysis of the influence of jitter on range measurement. 

Among the three contributions of this thesis, first, an algorithm for jitter extraction of a signal without access to a reference clock signal is proposed. The proposed algorithm is based upon Fourier analysis with signal processing techniques and it can be used for real time jitter extraction on a modulated signal with any kind of shape (sinusoidal, triangular, rectangular). The method is used to measure the amount of jitter in the light signals of two AMCW ToF range imaging cameras, namely, MESA Imaging SwissRanger 4000 and SoftKinetic DepthSense 325. Periodic and random jitter were found to be present in the light sources of both cameras with the MESA camera notably worse with random jitter of (159.6 +/- 0.1) ps RMS in amplitude.

Next, in a novel approach, an inexpensive software defined radio (SDR) USB dongle is used with the proposed algorithm to extract the jitter in the light signal of the above two ToF cameras. This is a cost effective alternative to the expensive real-time medium speed digital oscilloscope. However, it is shown that this method has some significant limitations, (1) it can measure the jitter only up to half of the intermediate-frequency obtained from the down shift of the amplified radio frequency with the local oscillator which is less than the Nyquist frequency of the dongle and (2) if the number of samples per cycle captured from this dongle is not sufficient then the jitter extraction  does not succeed since the signal is not properly (smoothly) represented.

Finally, the periodic and random jitter influence on range measurements made with AMCW range imaging cameras are studied. An analytical model for the periodic jitter on the range measurements under the heterodyne and homodyne operations in AMCW ToF range imaging cameras is obtained in the frequency domain. The analytical model is tested through simulated data with various parameters in the system. The product of angular modulation frequency of the camera and the amplitude of the periodic jitter is a characteristic parameter for the phase error due to the presence of periodic jitter. We found that for currently available AMCW cameras (modulation frequency less than 100 MHz), neither periodic nor random jitter has a measurable effect on range measurement. But with modulation frequency increases and integration period decreases likely in the near future, periodic jitter may have a measurable detection affect on ranging.

The influence of random jitter is also investigated by obtaining an analytical model based on stochastic calculus by using fundamental statistics and Fourier analysis. It is assumed that the random jitter  follows the Gaussian distribution. Monte Carlo simulation is performed on the model obtained for a 1 ms integration period. We found increasing the modulation frequency above approximately 400 MHz with random jitter of 140 ps has a measurable affect on ranging.

year: 2021

title: Technical note: A significance test for data-sparse zones in scatter plots

authors: Vetrova, V. V.

subjects: data-sparse zones

abstract: Data-sparse zones in scatter plots of hydrological variables can be of interest in various contexts. For example, a well-defined data-sparse zone may indicate inhibition of one variable by another. It is of interest therefore to determine whether data-sparse regions in scatter plots are of sufficient extent to be beyond random chance. We consider the specific situation of data-sparse regions defined by a linear internal boundary within a scatter plot defined over a rectangular region. An Excel VBA macro is provided for carrying out a randomisation-based significance test of the data-sparse region, taking into account both the within-region number of data points and the extent of the region. Example applications are given with respect to a rainfall time series from Israel and also to validation scatter plots from a seasonal forecasting model for lake inflows in New Zealand.

text: Technical note: A significance test for data-sparse zones in scatter plots Data-sparse zones in scatter plots of hydrological variables can be of interest in various contexts. For example, a well-defined data-sparse zone may indicate inhibition of one variable by another. It is of interest therefore to determine whether data-sparse regions in scatter plots are of sufficient extent to be beyond random chance. We consider the specific situation of data-sparse regions defined by a linear internal boundary within a scatter plot defined over a rectangular region. An Excel VBA macro is provided for carrying out a randomisation-based significance test of the data-sparse region, taking into account both the within-region number of data points and the extent of the region. Example applications are given with respect to a rainfall time series from Israel and also to validation scatter plots from a seasonal forecasting model for lake inflows in New Zealand.

year: 2012

title: In their voice: Adult learners' perspectives on literacy and numeracy, learning and wellbeing

authors: Furness, Jane Amanda

abstract: In their voice: Adult learners’ perspectives on literacy and numeracy, learning and wellbeing (2023) reports on a case study undertaken in collaboration with Literacy Aotearoa. It has been undertaken as part of a larger project, The expression, experience and transcendence of low skill in Aotearoa New Zealand (2019–2024), the aim of which is to provide policy recommendations to improve life-course trajectories and socio-economic outcomes for adults with low literacy and/or numeracy (L+N) skills in Aotearoa New Zealand (Aotearoa). In their voice: Adult learners’ perspectives on literacy and numeracy, learning and wellbeing examines adults’ experiences as they navigate their lives and develop their L+N repertoire towards their aspirations for themselves and their families. Our focus is mainly on Māori (the Indigenous peoples of Aotearoa) adults.

The study has taken place at a time when adult L+N policy is at a crossroads in three senses. Policy over the last 23 years has only marginally improved L+N on the measures government uses with adults, yet it is known that wide-ranging, holistic benefits accrue from L+N education that values and embodies Māori interests and ways of being. Second, the most recent iteration of L+N policy expired in 2017 and is yet to be replaced, opening an opportunity for reconceptualisation and transformation of adult L+N policy. Third, Māori educators have articulated and demonstrated over decades the content and approaches for L+N learning that are of interest and value to Māori adults and whānau (immediate and extended family) but these remain by-and-large systemically unsupported. Nevertheless, government expectation is that all policy in Aotearoa account for wellbeing outcomes as set out in the ‘Living Standards Framework ‘and ‘He Ara Waiora’ (The Treasury, 2021, n. d.).

The standpoint for this study is that the Eurocentric perspective of literacy that predominates in adult L+N policy in Aotearoa – reading and writing alphabetic text, usually in English, and primarily for economic purposes – is inadequate in our bicultural nation. This narrow view of literacy and its purposes severely limits the extent to which Māori expectations for adult L+N education and for Māori prosperity are realised, contrary to the word and the spirit of Te Tiriti o Waitangi (The Treaty of Waitangi). Viewing literacy through sociocultural, sociomaterial, critical literacies and Indigenous lenses, the study makes a strong case for a much broader understanding of literacy and its purposes to decolonise adult L+N policy for the future. Supporting this aspiration, the study advances the notion of multiple meanings of literacy in which Māori perspectives are valued, upheld and promoted. Māori perspectives are understood as centring on whakapapa (genealogy) which provides the framework for connectedness of all things and is the basis for Māori identity and for comprehending and interpreting the world. 

The research process was informed by Kaupapa Māori (a Māori agenda) to the extent possible. Māori researchers conducted all but one interview and contributed to the thematic analysis of participants’ narratives. Two Pākehā researchers worked closely with the Māori team members and were guided by them. The specific approach for this case study was co-designed with Literacy Aotearoa to ensure participants’ needs and aspirations in the research were met. Twenty adults (15 Māori, one Samoan and four Pākehā) graciously agreed to share their insights and were interviewed individually, in pairs or in a focus group according to their choice. They were aged from early 20s to late 60s and varied in their qualifications and learning challenges. The same number of men and women took part. The following questions directed the interviews and focus groups:

1. What has motivated people/whānau to make change in their lives?
2. What was the pathway that people/whānau have taken to make change in their lives? 
3. What are people’s experiences of their efforts to make change in their lives? 
4. What have been supports or facilitators, barriers or challenges in their efforts? 

The narrative transcripts were analysed from a critical sociocultural and strengths-based standpoint. Findings were described and discussed in relation to the following broad thematic categories:

 1. What matters to people in their lives – views of wellbeing, values and aspirations
 2. Learning and life pathways – experiences of learning, schooling and post school
 3. What enables people to live the lives they choose
 4. What makes it harder for people to live the lives they choose

The study shows the centrality of te ao Māori (Māori worldview) in the lives of Māori adults and whānau. It is fundamental to Māori identity and wellbeing and remains throughout their lives even when they have experienced periods of disconnection. Enacted valuing of te ao Māori within the programmes enabled participants to feel safe to be who they are, excited about their L+N learning, and looking forward to meaningful outcomes for themselves and their whānau despite the oft-present anxiety about returning to a classroom. Relatedly, prioritising the wellbeing of the learners through caring and respectful learning environments is crucial to coming to and staying in L+N learning opportunities which can then provide an opportunity to transcend hurtful past learning experiences and enable participants to see themselves as capable learners and contributing adults in the world. These characteristics of the participants’ learning experiences in the study programmes reflected values and ways of being fundamental to being Māori which meant the dissonance often experienced in other learning settings was not present and participants could enjoy learning what and how was important to them.

The study notes that L+N in the Eurocentric meaning was addressed in the L+N programmes our participants attended (for example digital skills for work were taught) but the programmes simultaneously embodied broader meanings and purposes of literacy that are not typically foregrounded in L+N policy in Aotearoa. The study contends that the enactment in the programmes of Māori values and ways of being and doing allowed transformative learning to occur, not just for the Māori learners but for everyone. The study demonstrated that L+N learning valued by learners themselves is best defined as the acquisition of knowledge and skills that have meaning and are useful in their lives, can contribute to better lives for whānau, hapū and iwi and can be passed on to future generations. Defined from this viewpoint, valued L+N includes matauranga Māori (Māori knowledge) and Māori cultural practices, values and language; foundational skills and knowledge in English missed at school; and specific skills for changing times including work and everyday personal, family and community life that centres whānau (family and extended family) wellbeing.

The study calls for a change in the definition and rationalisation embedded in current (though expired) adult L+N policy from a narrow economy-focused approach to a broad and culturally inclusive definition and rationalisation. This requires detachment from a singular view of what literacy is to a view of literacy as a multiple construct; in other words, seeing literacy as having many meanings. Accompanying this embrace of literacies, Māori perspectives of L+N must move from the margins of adult L+N policy to the centre, led by Māori.

text: In their voice: Adult learners' perspectives on literacy and numeracy, learning and wellbeing In their voice: Adult learners’ perspectives on literacy and numeracy, learning and wellbeing (2023) reports on a case study undertaken in collaboration with Literacy Aotearoa. It has been undertaken as part of a larger project, The expression, experience and transcendence of low skill in Aotearoa New Zealand (2019–2024), the aim of which is to provide policy recommendations to improve life-course trajectories and socio-economic outcomes for adults with low literacy and/or numeracy (L+N) skills in Aotearoa New Zealand (Aotearoa). In their voice: Adult learners’ perspectives on literacy and numeracy, learning and wellbeing examines adults’ experiences as they navigate their lives and develop their L+N repertoire towards their aspirations for themselves and their families. Our focus is mainly on Māori (the Indigenous peoples of Aotearoa) adults.

The study has taken place at a time when adult L+N policy is at a crossroads in three senses. Policy over the last 23 years has only marginally improved L+N on the measures government uses with adults, yet it is known that wide-ranging, holistic benefits accrue from L+N education that values and embodies Māori interests and ways of being. Second, the most recent iteration of L+N policy expired in 2017 and is yet to be replaced, opening an opportunity for reconceptualisation and transformation of adult L+N policy. Third, Māori educators have articulated and demonstrated over decades the content and approaches for L+N learning that are of interest and value to Māori adults and whānau (immediate and extended family) but these remain by-and-large systemically unsupported. Nevertheless, government expectation is that all policy in Aotearoa account for wellbeing outcomes as set out in the ‘Living Standards Framework ‘and ‘He Ara Waiora’ (The Treasury, 2021, n. d.).

The standpoint for this study is that the Eurocentric perspective of literacy that predominates in adult L+N policy in Aotearoa – reading and writing alphabetic text, usually in English, and primarily for economic purposes – is inadequate in our bicultural nation. This narrow view of literacy and its purposes severely limits the extent to which Māori expectations for adult L+N education and for Māori prosperity are realised, contrary to the word and the spirit of Te Tiriti o Waitangi (The Treaty of Waitangi). Viewing literacy through sociocultural, sociomaterial, critical literacies and Indigenous lenses, the study makes a strong case for a much broader understanding of literacy and its purposes to decolonise adult L+N policy for the future. Supporting this aspiration, the study advances the notion of multiple meanings of literacy in which Māori perspectives are valued, upheld and promoted. Māori perspectives are understood as centring on whakapapa (genealogy) which provides the framework for connectedness of all things and is the basis for Māori identity and for comprehending and interpreting the world. 

The research process was informed by Kaupapa Māori (a Māori agenda) to the extent possible. Māori researchers conducted all but one interview and contributed to the thematic analysis of participants’ narratives. Two Pākehā researchers worked closely with the Māori team members and were guided by them. The specific approach for this case study was co-designed with Literacy Aotearoa to ensure participants’ needs and aspirations in the research were met. Twenty adults (15 Māori, one Samoan and four Pākehā) graciously agreed to share their insights and were interviewed individually, in pairs or in a focus group according to their choice. They were aged from early 20s to late 60s and varied in their qualifications and learning challenges. The same number of men and women took part. The following questions directed the interviews and focus groups:

1. What has motivated people/whānau to make change in their lives?
2. What was the pathway that people/whānau have taken to make change in their lives? 
3. What are people’s experiences of their efforts to make change in their lives? 
4. What have been supports or facilitators, barriers or challenges in their efforts? 

The narrative transcripts were analysed from a critical sociocultural and strengths-based standpoint. Findings were described and discussed in relation to the following broad thematic categories:

 1. What matters to people in their lives – views of wellbeing, values and aspirations
 2. Learning and life pathways – experiences of learning, schooling and post school
 3. What enables people to live the lives they choose
 4. What makes it harder for people to live the lives they choose

The study shows the centrality of te ao Māori (Māori worldview) in the lives of Māori adults and whānau. It is fundamental to Māori identity and wellbeing and remains throughout their lives even when they have experienced periods of disconnection. Enacted valuing of te ao Māori within the programmes enabled participants to feel safe to be who they are, excited about their L+N learning, and looking forward to meaningful outcomes for themselves and their whānau despite the oft-present anxiety about returning to a classroom. Relatedly, prioritising the wellbeing of the learners through caring and respectful learning environments is crucial to coming to and staying in L+N learning opportunities which can then provide an opportunity to transcend hurtful past learning experiences and enable participants to see themselves as capable learners and contributing adults in the world. These characteristics of the participants’ learning experiences in the study programmes reflected values and ways of being fundamental to being Māori which meant the dissonance often experienced in other learning settings was not present and participants could enjoy learning what and how was important to them.

The study notes that L+N in the Eurocentric meaning was addressed in the L+N programmes our participants attended (for example digital skills for work were taught) but the programmes simultaneously embodied broader meanings and purposes of literacy that are not typically foregrounded in L+N policy in Aotearoa. The study contends that the enactment in the programmes of Māori values and ways of being and doing allowed transformative learning to occur, not just for the Māori learners but for everyone. The study demonstrated that L+N learning valued by learners themselves is best defined as the acquisition of knowledge and skills that have meaning and are useful in their lives, can contribute to better lives for whānau, hapū and iwi and can be passed on to future generations. Defined from this viewpoint, valued L+N includes matauranga Māori (Māori knowledge) and Māori cultural practices, values and language; foundational skills and knowledge in English missed at school; and specific skills for changing times including work and everyday personal, family and community life that centres whānau (family and extended family) wellbeing.

The study calls for a change in the definition and rationalisation embedded in current (though expired) adult L+N policy from a narrow economy-focused approach to a broad and culturally inclusive definition and rationalisation. This requires detachment from a singular view of what literacy is to a view of literacy as a multiple construct; in other words, seeing literacy as having many meanings. Accompanying this embrace of literacies, Māori perspectives of L+N must move from the margins of adult L+N policy to the centre, led by Māori.

year: 2023