Dr. Otto P. Hasekamp Profile

Dr. Otto P. Hasekamp

at SRON Netherlands Institute for Space Research

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Author

Publications (14)

Proceedings Article | 12 July 2023 Open Access

SPEXone multi-angle spectropolarimeter characterization, calibration, and key data derivation using the L0-1B processor

Jeroen Rietjens, Martijn Smit, Jochen Campo, Thomas Bouchan, Ryan Cooney, Pierre Piron, Paul Tol, Raul Laasner, Richard van Hees, Jochen Landgraf, Otto Hasekamp

Proceedings Volume 12777, 127774U (2023) https://doi.org/10.1117/12.2690892

KEYWORDS: Calibration, Equipment, Stray light, Polarimetry, Polarization, Data processing, Spectropolarimetry, Radiometric calibration, Data communications, Astronomical imaging

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In the past few years, the SPEXone instrument has been developed, tested, calibrated and delivered to the NASA PACE (Plankton Aerosol and Ocean Ecosystems) project by a Dutch consortium consisting of SRON and Airbus Defence and Space Netherlands with support from TNO. Onboard the PACE satellite, SPEXone will fly together with the Ocean Color Instrument (OCI) and the Hyper-Angular Rainbow Polarimeter 2 (HARP2). SPEXone is a compact multi-angle channeled spectropolarimeter with five viewing angles and hyperspectral imaging of a ⇠100 km swath with a spatial resolution of 4.6 ⇥ 5.4 km in the along-track and across-track directions and a spatial oversampling ratio of 2. SPEXone has a spectral range from 385 to 770 nm and a spectral resolution slightly below 2 nm. High accuracy polarimetry is achieved by implementation of the dual-beam snapshot spectral polarization modulation concept, yielding two complementary spectrally modulated hyperspectral images of the same scene from which both radiance and state of linear polarization can be extracted. This paper presents results from the characterization and on-ground calibration campaign of SPEXone and discusses the use of the L0-L1B processor to derive the calibration key data (CKD) that is required for the operational data processing. The L0-L1B data processor has been developed in such a way that the CKD derivation is fully consistent with the L0-L1B processing steps, meaning that the data from which the CKD at a certain processing step is derived has been processed using the CKD from all previous processing steps. The processing steps that have been implemented include those related to the detector characterization (dark o↵set and dark current, non-linearity, and pixel-response non-uniformity), and those related to the instrument calibration (stray light, field-of-view, line-of-sight, wavelength, radiometric and polarimetric). We will show examples of the derived CKD and their use in the processing of measurement data. We will demonstrate the performance of the polarimetric calibration by comparing SPEXone measurement results against a well characterized polarization state generator, showing di↵erences of the order of a few times 0.001 in the degree of linear polarization. In addition, we will discuss the approach for the implementation of a stray light correction algorithm that has the potential to correct di↵use stray light with a spectral intensity and possibly size variation of the kernel, and that can correct moving ghosts with a constant kernel shape.

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Proceedings Article | 11 June 2021 Open Access

Polarimetric calibration of a spectro-polarimeter for remote sensing and characterization of aerosols

Martijn Smit, Jeroen Rietjens, Jochen Campo, Joost aan de Brugh, Aaldert van Amerongen, Otto Hasekamp, Jochen Landgraf, Xin Liu

Proceedings Volume 11852, 1185232 (2021) https://doi.org/10.1117/12.2599475

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High accuracy multi-angle polarimetry is of crucial importance for remote sensing of aerosol properties with accuracies demanded by climate and air quality studies. In this contribution, we discuss the polarimetric calibration of the multi-angle polarimeter "SPEX airborne". SPEX airborne is a multi-angle viewing instrument providing snapshot measurements of spectral radiance and degree of linear polarization at fixed viewing angles. Radiance and polarization are measured as a continuous function of wavelength in the 400-760nm range, at nine viewing angles equally distributed over an angular range of -56° to +56°. Each viewing-angle aperture has a swath of 7° with an instantaneous field of view of 0.5°l° (cross- times along-track). SPEX airborne measures the degree and angle of linear polarization of scattered sunlight by means of spectral modulation. For each field of view, the instrument records two modulated spectra. Ideally, these are perfectly in anti-phase, such that the sum of the modulated spectra is modulation free and gives the spectral radiance. The state of linear polarization is derived from the scaled difference of the modulated spectra. As a result of finite image quality at the focal plane, any spectropolarimeter using spectral modulation will show different polarimetric responses for the two modulated spectra, which breaks the anti-phase symmetry. For SPEX airborne this is indeed the case, and special care is taken both in the calibration and in the data processing. Ignoring this can lead to errors both in polarimetric and radiometric measurements. It is shown however that these errors are quite small. In this contribution, we will outline the spectral modulation technique employed by SPEX airborne to measure the state of linear polarization, explain which instrumental parameters are to be determined by calibration and how they feature in the data processing chain. We discuss the polarization calibration setup and how polarization calibration measurements are processed into useful calibration data. Taking a Mueller matrix approach, we show how differences in polarimetric responses can be mitigated, while also other imperfections like telescope polarization are accounted for without extra calibration effort. We also present a scheme to correct for sharp features in the solar spectrum, which would otherwise mix into the modulation spectra via the finite slit-width of the spectrometer and result in polarimetric errors. The effect of telescope polarization is also discussed Polarimetric calibration of SPEX airborne is relevant for SPEXone, a compact multi-angle polarimeter that builds on SPEX airborne heritage and space-borne spectrometer heritage within the Netherlands. SPEXone has been developed for NASA's PACE mission, which has a planned launch date in 2023.

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Proceedings Article | 11 June 2021 Open Access

Characterization and video chain development of the CMOS detector applied in the multi-angle spectro-polarimeter SPEXone

Jochen Campo, Paul Tol, Joris van der Vlugt, Martijn Smit, Jelle Talsma, Jens Johansen, Alexander Eigenraam, Richard van Hees, Otto Hasekamp, Marc Oort, Aaldert van Amerongen, Jeroen Rietjens

Proceedings Volume 11852, 1185213 (2021) https://doi.org/10.1117/12.2599224

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Proceedings Article | 11 June 2021 Open Access

Optical and system performance of SPEXone, a multi-angle channeled spectropolarimeter for the NASA PACE mission

Jeroen H. Rietjens, Jochen Campo, Martijn Smit, Robbert Winkelman, Raj Nalla, Jochen Landgraf, Otto Hasekamp, Marc Oort, Aaldert van Amerongen

Proceedings Volume 11852, 1185234 (2021) https://doi.org/10.1117/12.2599531

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SPEXone is a multi-angle channeled spectropolarimeter that is developed by a Dutch consortium consisting of SRON and Airbus Defence and Space Netherlands with support from TNO. SPEXone will fly together with the Ocean Color Instrument (OCI) and the Hyper-Angular Rainbow Polarimeter-2 (HARP-2) on the NASA Plankton, Aerosol, Clouds and ocean Ecosystem (PACE) mission, which has a notional launch in 2023. SPEXone will deliver high quality hyperspectral multi-angle radiance and polarization products that, together with products from OCI and HARP2, enable unprecedented aerosol and cloud characterization from space. SPEXone employs dual beam spectral polarization modulation, in which the state of linear polarization is encoded in a spectrum as a periodic variation of the intensity. This technique enables high polarimetric accuracies in operational environments, since it provides snapshot acquisition of both radiance and polarization without moving parts. SPEXone has five viewing angles that are realized using a novel three-mirror segmented telescope assembly. The telescope focuses light captured by the five viewing angles onto a single image plane consisting of five stacked sub-slits. This multi-slit forms the entrance slit of a reflective grating spectrometer that consists of freeform mirrors and an order-sorting filter close to the focal plane, yielding an intrinsic spectral resolution of 2 nm and 5.4 km spatial resolution across the 100 km swath. The spectrometer re-images two spectral images per viewing angle following a dual beam spectral polarization modulation implementation. In this contribution, the optical performance of the telescope and spectrometer will be presented by means of star stimulus measurements at the slit plane and at the spectrometer focal plane. Measurements of the optical spot quality and preliminary measurements of stray light are compared with the optical design and with stray light simulations. We find that the measured optical performance of the telescope and spectrometer is better than modelled, showing higher resolution and lower slit keystone, thereby meeting all spatial and spectral resolution requirements. Also, preliminary stray light results indicate a higher diffuse but lower ghost contribution to the total stray light, which is in general beneficial for implementing stray light correction, which will enhance the polarimetric accuracy in inhomogeneous scenes.

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Proceedings Article | 6 September 2019 Paper

Expected performance and error analysis for SPEXone, a multi-angle channeled spectropolarimeter for the NASA PACE mission

Jeroen Rietjens, Jochen Campo, Anantha Chanumolu, Martijn Smit, Raj Nalla, Cristina Fernandez, Jos Dingjan, Aaldert van Amerongen, Otto Hasekamp

Proceedings Volume 11132, 1113208 (2019) https://doi.org/10.1117/12.2530729

KEYWORDS: Polarimetry, Error analysis, Polarization, Modulation, Aerosols, Environmental sensing, Atmospheric corrections, Atmospheric particles, Aerospace engineering, Space operations

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SPEXone is a compact five–angle spectropolarimeter that is being developed as a contributed payload for the NASA Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) observatory, to be launched in 2022. SPEXone will provide accurate atmospheric aerosol characterization from space for climate research, as well as for light path correction in support of the main Ocean Color Instrument. SPEXone employs dual beam spectral polarization modulation, in which the state of linear polarization is encoded in a spectrum as a periodic variation of the intensity. This technique enables high polarimetric accuracies in operational environments, since it provides snapshot acquisition of both radiance and polarization without moving parts. This paper presents the polarimetric error analysis and budget for SPEXone in terms of polarimetric precision and polarimetric accuracy. We consider factors that contribute to instrumental polarization and modulation efficiency, which will be calibrated on-ground with high, but finite accuracy. The sensitivity to dynamic systematic effects in a space environment, such as degradation and ageing of components and small variations in the temperature and thermal gradients is addressed and quantified. Finally, the impact of scene dependent error sources, mainly resulting from stray light, are assessed and the total polarimetric error budget is presented. We show that SPEXone complies with the radiometric SNR requirement of 300, yielding a minimum polarimetric precision of 200 (fully polarized light) to 300 (unpolarized light) over the full spectral range for dark ocean scenes at high solar zenith angle. Assuming a stray light correction factor of 5 and considering a moderate contrast scene, the expected in-flight polarimetric accuracy of SPEXone is 1.5 · 10⁻³ for unpolarized scenes and 2.9 · 10⁻³ for highly polarized scenes, compliant with the polarimetric accuracy requirement. This performance should enable SPEXone to deliver the data quality that enables unprecedented aerosol characterization from space on the NASA PACE mission.

Proceedings Article | 12 July 2019 Open Access

In-flight validation of SPEX airborne spectro-polarimeter onboard NASA's research aircraft ER-2

J. Martijn Smit, Jeroen H. Rietjens, Antonio di Noia, Otto Hasekamp, Wouter Laauwen, Brian Cairns, Bastiaan van Diedenhoven, A. Wasilewski

Proceedings Volume 11180, 111800N (2019) https://doi.org/10.1117/12.2535942

KEYWORDS: Polarization, Polarimetry, Calibration, Modulation, Clouds, Aerosols, Cameras, Spectroscopy, Ocean optics, Mirrors

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Proceedings Article | 12 July 2019 Open Access

SPEXone: a compact multi-angle polarimeter

Aaldert van Amerongen, Jeroen Rietjens, Jochen Campo, Ersin Dogan, Jos Dingjan, Raj Nalla, Jerome Caron, Otto Hasekamp

Proceedings Volume 11180, 111800L (2019) https://doi.org/10.1117/12.2535940

KEYWORDS: Aerosols, Telescopes, Mirrors, Sensors, Spectroscopy, Polarization, Modulation, Ocean optics, Optics manufacturing, Polarimetry

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We have developed a 6 dm³-sized optical instrument to characterize the microphysical properties of fine particulate matter or aerosol in the Earth atmosphere from low Earth orbit. Our instrument can provide detailed and worldwide knowledge of aerosol amount, type and properties. This is important for climate and ecosystem science and human health [1, 2]. Therefore, NASA, ESA and the European Commission study the application of aerosol instruments for planned or future missions. We distinguish molecular Rayleigh scattering from aerosol Mie-type scattering by analyzing multi-angle observations of radiance and the polarization state of sun light that is scattered in the Earth atmosphere [3]. We measure across the visible wavelength spectrum and in five distinct viewing angles between -50° and +50°. Such analysis has been traditionally done by rotating polarizers and band-filters in front of an Earth observing wide-angle imager. In contrast, we adopt a means to map the linear polarization state on the spectrum using passive optical components [4]. Thereby we can characterize the full linear polarization state for a scene instantaneously. This improves the polarimetric accuracy, which is critical for aerosol characterization, enabling us to distinguish for example anthropogenic from natural aerosol types. Moreover, the absence of moving parts simplifies the instrument, and makes it more robust and reliable. We have demonstrated this method in an airborne instrument called SPEX airborne [5, 6] in the recent ACEPOL campaign together with a suite of state-of-the art and innovative active and passive aerosol sensors on the NASA ER-2 high-altitude research platform [7]. An earlier report on the SPEX development roadmap was given in [8]. In this contribution we introduce SPEXone, a compact space instrument that has a new telescope that projects the five viewing angles onto a single polarization modulation unit and the subsequent reflective spectrometer. The novel telescope allows the observation of five scenes with one spectrometer, hence the name. We describe the optical layout of the telescope, polarization modulation optics, and spectrometer and discuss the manufacturability and tolerances involved. We will also discuss the modelled instrument performance and show preliminary results from optical breadboards of the telescope and polarization modulation optics. With SPEXone we present a strong and new tool for climate research and air quality monitoring. It can be used to study the effect of atmospheric aerosol on the heating/cooling of the Earth and on air quality. Also, SPEXone can improve the accuracy of satellite measurements of greenhouse gas concentrations and ocean color that rely on molecular absorption of reflected sunlight by providing detailed knowledge of the aerosol properties, required to accurately trace the light path in presence of scattering.
SPEXone is developed in a partnership between SRON Netherlands Institute for Space Research and Airbus Defence and Space Netherlands with support from the Netherlands Organisation for Applied Scientific Research (TNO) as a Dutch contribution to the NASA PACE observatory launching in 2022.

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Proceedings Article | 20 November 2017 Open Access

Spectropolarimetry for earth observations: a novel method for characterization of aerosols and clouds

Oana Van der Togt, Ad Verlaan, Kees Moddemeijer, Martijn Smit, Jeroen Rietjens, Otto Hasekamp, Daphne Stam, Frans Snik, Gerard van Harten

Proceedings Volume 10564, 105641S (2017) https://doi.org/10.1117/12.2309041

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Proceedings Article | 17 November 2017 Open Access

SPEX: a highly accurate spectropolarimeter for atmospheric aerosol characterization

J. H. Rietjens, J. Smit, A. di Noia, O. Hasekamp, G. van Harten, F. Snik, C. Keller

Proceedings Volume 10563, 1056344 (2017) https://doi.org/10.1117/12.2304227

KEYWORDS: Aerosols, Polarimetry, Polarization, Scattering, Modulation, Atmospheric particles, Prototyping, Glasses, Astronomical imaging, Refractive index

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Global characterization of atmospheric aerosol in terms of the microphysical properties of the particles is essential for understanding the role aerosols in Earth climate [1]. For more accurate predictions of future climate the uncertainties of the net radiative forcing of aerosols in the Earth’s atmosphere must be reduced [2]. Essential parameters that are needed as input in climate models are not only the aerosol optical thickness (AOT), but also particle specific properties such as the aerosol mean size, the single scattering albedo (SSA) and the complex refractive index. The latter can be used to discriminate between absorbing and non-absorbing aerosol types, and between natural and anthropogenic aerosol. Classification of aerosol types is also very important for air-quality and health-related issues [3].

Remote sensing from an orbiting satellite platform is the only way to globally characterize atmospheric aerosol at a relevant timescale of ∼ 1 day [4]. One of the few methods that can be employed for measuring the microphysical properties of aerosols is to observe both radiance and degree of linear polarization of sunlight scattered in the Earth atmosphere under different viewing directions [5][6][7]. The requirement on the absolute accuracy of the degree of linear polarization P_L is very stringent: the absolute error in P_L must be smaller then 0.001+0.005⋅P_L in order to retrieve aerosol parameters with sufficient accuracy to advance climate modelling and to enable discrimination of aerosol types based on their refractive index for air-quality studies [6][7].

In this paper we present the SPEX instrument, which is a multi-angle spectropolarimeter that can comply with the polarimetric accuracy needed for characterizing aerosols in the Earth’s atmosphere. We describe the implementation of spectral polarization modulation in a prototype instrument of SPEX and show results of ground based measurements from which aerosol microphysical properties are retrieved.

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Proceedings Article | 25 September 2017 Open Access

Spex the Dutch roadmap towards aerosol measurement from space

Aaldert van Amerongen, Jeroen Rietjens, Martijn Smit, Dennis van Loon, Hedser van Brug, Wencke van der Meulen, Marco Esposito, Otto Hasekamp

Proceedings Volume 10562, 105621O (2017) https://doi.org/10.1117/12.2296227

KEYWORDS: Aerosols, Polarization, Modulation, Sensors, Clouds, Polarimetry, Signal to noise ratio, Prototyping, Atmospheric modeling, Astronomical imaging

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Proceedings Article | 1 September 2015 Paper

Accurate spectrally modulating polarimeters for atmospheric aerosol characterization

Jeroen Rietjens, Martijn Smit, Gerard van Harten, Antonio Di Noia, Otto Hasekamp, Jos de Boer, Hester Volten, Frans Snik, Christoph Keller

Proceedings Volume 9613, 96130S (2015) https://doi.org/10.1117/12.2188024

KEYWORDS: Aerosols, Prototyping, Polarization, Modulation, Polarimetry, Atmospheric particles, Observatories, Spectrographs, Refractive index, Earth's atmosphere

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Proceedings Article | 10 September 2011 Paper

Prototyping for the Spectropolarimeter for Planetary EXploration (SPEX): calibration and sky measurements

Gerard van Harten, Frans Snik, Jeroen H. Rietjens, J. Martijn Smit, Jozua de Boer, Renia Diamantopoulou, Otto Hasekamp, Daphne Stam, Christoph Keller, Erik Laan, Ad Verlaan, Willem Vliegenthart, Rik ter Horst, Ramón Navarro, Klaas Wielinga, Sandro Hannemann, Scott Moon, Robert Voors

Proceedings Volume 8160, 81600Z (2011) https://doi.org/10.1117/12.893741

KEYWORDS: Polarization, Aerosols, Prototyping, Modulation, Atmospheric particles, Polarimetry, Calibration, Wave plates, Scattering, Climatology

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We present the Spectropolarimeter for Planetary EXploration (SPEX), a high-accuracy linear spectropolarimeter measuring from 400 to 800 nm (with 2 nm intensity resolution), that is compact (~ 1 liter), robust and lightweight. This is achieved by employing the unconventional spectral polarization modulation technique, optimized for linear polarimetry. The polarization modulator consists of an achromatic quarter-wave retarder and a multiple-order retarder, followed by a polarizing beamsplitter, such that the incoming polarization state is encoded as a sinusoidal modulation in the intensity spectrum, where the amplitude scales with the degree of linear polarization, and the phase is determined by the angle of linear polarization. An optimized combination of birefringent crystals creates an athermal multiple-order retarder, with a uniform retardance across the field of view. Based on these specifications, SPEX is an ideal, passive remote sensing instrument for characterizing planetary atmospheres from an orbiting, air-borne or ground-based platform. By measuring the intensity and polarization spectra of sunlight that is scattered in the planetary atmosphere as a function of the single scattering angle, aerosol microphysical properties (size, shape, composition), vertical distribution and optical thickness can be derived. Such information is essential to fully understand the climate of a planet. A functional SPEX prototype has been developed and calibrated, showing excellent agreement with end-to-end performance simulations. Calibration tests show that the precision of the polarization measurements is at least 2 • 10^-4. We performed multi-angle spectropolarimetric measurements of the Earth's atmosphere from the ground in conjunction with one of AERONET's sun photometers. Several applications exist for SPEX throughout the solar system, a.o. in orbit around Mars, Jupiter and the Earth, and SPEX can also be part of a ground-based aerosol monitoring network.

Proceedings Article | 21 October 2005 Paper

Spectrograph dedicated to measuring tropospheric trace gas constituents from space

Johan de Vries, Erik Laan, Alex Deutz, Isabel Escudero-Sanz, Henk Bokhove, Jan Hoegee, Ilse Aben, Rienk Jongma, Jochen Landgraf, Otto Hasekamp, Sander Houweling, Michiel van Weele, Roeland van Oss, Gijsbertus van den Oord, Pieternel Levelt

Proceedings Volume 5978, 59780O (2005) https://doi.org/10.1117/12.627008

KEYWORDS: Aerosols, Clouds, Sensors, Short wave infrared radiation, Satellites, Carbon monoxide, Climatology, Ozone, Aerospace engineering, Gases

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Proceedings Article | 30 November 2004 Paper

Satellite remote sensing of aerosols: information content of different measurement types

Otto Hasekamp, Jochen Landgraf

Proceedings Volume 5571, (2004) https://doi.org/10.1117/12.566374

KEYWORDS: Aerosols, Atmospheric modeling, Polarization, Radiative transfer, Satellites, Refractive index, Atmospheric particles, Remote sensing, Scattering, Mie scattering

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