Christian Matzler

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• Professor, Dr. phil. nat.
• Professor at University of Bern

The dependence of L-band Vegetation Optical Depth (L-VOD, τ) on Vegetation temperature TV is investigated for 1165 boreal forest grid cells selected for latitudes > 55◦ and high radiometric forest fraction FFO ≥ 90%. SMOS Level-3 Brightness Temperatures (BT) at ascending orbits acquired from 2011 to 2022 are used. This is a spatio- temporal extensi...

To better understand the interactions between C-band radar waves and snow, a tower-based experiment was set up in the Idaho Rocky Mountains for the period of 2021–2023. The experiment objective was to improve understanding of the sensitivity of Sentinel-1 C-band backscatter radar signals to snow. The data were collected in the time domain to measur...

Assessing the Surface Mass Balance (SMB) of the Antarctic Ice Sheet is crucial for understanding its response to climate change. Synthetic Aperture Radar observations from Sentinel-1 provide the potential to monitor the variability of SMB processes through changes in the scattering response of near-surface and internal snow layers. However, the int...

To better understand the interactions between C-band radar waves and snow, a tower-based experiment was set up in the Idaho Rocky Mountains for the period of 2021–2023. The experiment objective was to improve understanding of the sensitivity of Sentinel-1 C-band backscatter radar signals to snow. The data were collected in the time domain to measur...

Microwave remote sensing of the cryosphere demands a formulation of the scattering coefficient which can be applied over the entire range of relevant densities, from fresh snow to bubbly ice, at all frequencies and for any grain size and snow type. Most challenging are intermediate densities (450–550 kgm-3) and high frequencies (or coarse-grained s...

Microwave remote sensing of the cryosphere demands a formulation of the scattering coefficient which can be applied over the entire range of relevant densities, from fresh snow to bubbly ice, at all frequencies and for any grain size and snow type. Most challenging are intermediate densities (450–550 kg m−3) and high frequencies (or coarse-grained...

This study reports on four consecutive winter campaigns (2016-2020) at the 'Davos-Laret Remote Sensing Field Laboratory' in the Swiss Alps to gain insight into the L-band microwave emission of ground covered with seasonal snow. Close-range L-band Brightness temperatures TB p,φ (θ) were measured over the site scanning different observation nadir ang...

This article experimentally investigates relationships between copol backscattering at a wide range of frequencies (L- to Ka-bands) and snow-ground state parameters (SPs) in different evolution phases during the full winter cycle of 2019/2020. Backscattering coefficients from 1 to 40 GHz, in situ snow-ground SPs, and meteorological data are measure...

Water vapor column density, or vertically-integrated water vapor (IWV), is monitored by ground-based microwave radiometers (MWR) and ground-based receivers of the Global Navigation Satellite System (GNSS). For rain periods, the retrieval of IWV from GNSS Zenith Wet Delay (ZWD) neglects the atmospheric propagation delay of the GNSS signal by rain dr...

ElectroMagnetic (EM) reasons resulting in temperature dependence of L-band Vegetation Optical Depth (L-VOD) are currently overlooked in remote sensing products. Discrepancies in retrievals of geophysical surface properties over vegetated areas can result from this incompleteness. This perception motivated to explore EM considerations in how tempera...

The modular Snow Microwave Radiative Transfer (SMRT) model simulates microwave scattering behavior in snow via different selectable theories and snow microstructure representations, which is well suited to intercomparisons analyses. Here, five microstructure models were parameterized from X-ray tomography and thin-section images of snow samples and...

Because of its clear physical meaning, physical methods are more often used for space-borne microwave radiometers to retrieve the rain rate, but they are rarely used for ground-based microwave radiometers that are very sensitive to rainfall. In this article, an opacity physical retrieval method is implemented to retrieve the rain rate (denoted as O...

Reliable microstructure measurement of snow is a requirement for microwave radiative transfer model validation. Snow specific surface area (SSA) can be measured using stereological methods, in which snow samples are cast in the field and photographed in the laboratory. Processing stereology photographs manually by counting intersections of test cyc...

Understanding surface melt over the Greenland Ice Sheet (GrIS) is important for evaluating the effect of the changing global climate on humanity, and for forecasting sea level rise. We demonstrate a recently developed L-band passive microwave algorithm for the retrieval of snow liquid water and snow and firn density over the GrIS. The retrievals ar...

Vertically integrated water vapour (IWV) is expected to increase globally in a warming climate. To determine whether IWV increases as expected on a regional scale, we present IWV trends in Switzerland from ground-based remote sensing techniques and reanalysis models, considering data for the time period 1995 to 2018. We estimate IWV trends from a g...

Abstract. Vertically integrated water vapour (IWV) is expected to increase globally in a warming climate. To determine whether IWV increases as expected on a regional scale, we present IWV trends in Switzerland from ground-based remote sensing techniques and reanalysis models, considering data for the time period 1995 to 2018. We estimate IWV trend...

The TROpospheric WAter RAdiometer (TROWARA) continuously measures integrated water vapour (IWV) with a time resolution of 6 s at Bern in Switzerland. During summer, we often see that IWV has temporal fluctuations during daytime, while the nighttime data are without fluctuations. The data analysis is focused on the year 2010, where TROWARA has a goo...

Fig. 1. a) Setup of the Emission Models EM = {TO, 2S} used to simulate ,,, , of a rough soil surface covered by a vegetation layer. b) How TO EM and 2S EM represent downwelling radiation emitted by vegetation. Abstract-An Emission Models (EM) adequate for a retrieval algorithm requires being simple while still capturing the responses of brightness...

The TROpospheric WAter RAdiometer (TROWARA) continuously measures integrated water vapour (IWV) with a time resolution of 6 seconds at Bern in Switzerland. During summer, we often see that IWV has temporal fluctuations during daytime while the night-time data are without fluctuations. The data analysis is focused on the year 2010 where TROWARA has...

Microwave Emission Models (EM) are used in retrieval algorithms to estimate geophysical state parameters such as soil Water Content ( W C ) and vegetation optical depth ( τ ), from brightness temperatures T B p , θ measured at nadir angles θ at Horizontal and Vertical polarizations p = { H , V } . An EM adequate for implementation in a retrieval al...

The MATLAB files can be downloaded from the following website: http://www.iap.unibe.ch/publications/pub-detail.php?lang=en&id=4783 ***************************************************************************************** Abstract: A set of functions has been developed in MATLAB to retrieve refractive indices from aerosol particle extinction spect...

The L-band radiometry data and in-situ ground and snow measurements performed during the 2016/2017 winter campaign at the Davos-Laret remote sensing field laboratory are presented and discussed. An improved version of the procedure for the computation of L-band brightness temperatures from ELBARA radiometer raw data is introduced. This procedure in...

Cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) were continuously measured from 2004 to 2016 by the TROpospheric WAter RAdiometer (TROWARA) in Bern, Switzerland. There are indications for interannual variations of CF and ILW. A spectral analysis shows that IWV is dominated by an annual oscillation, leading to an...

The TROpospheric WAter RAdiometer (TROWARA) is a ground-based microwave radiometer with an additional infrared channel observing atmospheric water parameters in Bern, Switzerland. TROWARA measures with nearly all-weather capability during day- and nighttime with a high temporal resolution (about 10 s). Using the almost complete data set from 2004 t...

Cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) were continuously measured from 2004 to 2016 by the TROpospheric WAter RAdiometer (TROWARA) at Bern in Switzerland. There are indications for inter-annual variations of CF and ILW while the IWV series of annual means mainly shows a positive linear trend. A spectral...

Aboveground dry snow influences the L-band ground–snow system emissivity as the result of impedance matching and refraction effects. Against this background, a retrieval scheme was proposed to estimate dry-snow density and ground permittivity from passive L-band measurements. In this study, the sensitivity of the recently proposed retrieval scheme...

Cloud fraction (CF) plays a crucial role in the Earth’s radiative energy budget and thus in the climate. Reliable long-term measurements of CF are rare. The ground-based TROpospheric WAter RAdiometer (TROWARA) at Bern, Switzerland continuously measures integrated liquid water and infrared brightness temperature with a time resolution of 6–11 s sinc...

The objective of the Nordic Snow Radar Experiment (NoSREx) campaign was to provide a continuous time series of active and passive microwave observations of snow cover at a representative location of the Arctic boreal forest area, covering a whole winter season. The activity was a part of Phase A studies for the ESA Earth Explorer 7 candidate missio...

European Space Agency's SnowScat instrument is a real aperture scatterometer which was developed by Gamma Remote Sensing AG. It operates in a continuous-wave mode, covers a frequency range of 9.15–17.9 GHz in a user-defined frequency-step and has a full polarimetric capability. The measurement campaigns were started first in February 2009 at Weissf...

The objective of the Nordic Snow Radar Experiment (NoSREx) campaign was to provide a continuous time series of active and passive microwave observations of snow cover in a representative location of the Arctic boreal forest area, covering a whole winter season. The activity was a part of Phase A studies for the ESA Earth Explorer 7 candidate missio...

In a combined experimental and model study, we investigated effects of surface topography (relief) on the thermal L-band emission of a sandy soil. To this end, brightness temperatures of two adjacent footprint areas were measured quasi-simultaneously with an L-band radiometer at the observation angle of 55° relative to nadir for one year. One footp...

The Microwave Emission Model of Layered Snowpacks (MEMLS) was originally developed for microwave emissions of snowpacks in the frequency range 5–100 GHz. It is based on six-flux theory to describe radiative transfer in snow including absorption, multiple volume scattering, radiation trapping due to internal reflection and a combination of coherent...

A synthetic study was performed to determine the potential to retrieve dry-snow density and ground permittivity from multiangular L-band brightness temperatures. The thereto employed emission model was developed from parts of the “microwave emission model of layered snowpacks” (MEMLS) coupled with components adopted from the “L-band microwave emiss...

An unusual ice type, called hair ice, grows on the surface of dead wood of broad-leaf trees at temperatures slightly below 0 °C. We describe this phenomenon and present physical, chemical, and biological investigations to gain insight in the properties and processes related to hair ice. Tests revealed that the biological activity of a winter-active...

Remote sensing of snow with active and passive microwaves on terrestrial, aerial, and satellite platforms has a long tradition. However, the observation of dynamic processes on alpine slopes is difficult due to fixed satellite orbits and consequently given observation geometry and interval and in some cases, also the lack of spatial resolution. Fur...

An unusual ice type, called hair ice, grows on the surface of dead wood of broad-leaf trees at temperatures slightly below 0 °C. We describe this phenomenon and present physical, chemical, and biological investigations to gain insight in the properties and processes related to hair ice. Tests revealed that the biological activity of a winter-active...

Cloud fraction (CF) is known as the dominant modulator of Earth's radiative fluxes. Ground-based CF observations are useful to characterize the cloudiness of a specific site and are valuable for comparison with satellite observations and numerical models. We present for the first time CF statistics (relative to liquid clouds only) for Bern, Switzer...

The microwave radiometer TROWARA measures integrated water vapour (IWV) and integrated cloud liquid water (ILW) at Bern since 1994 with a time resolution of 7 s. In this study, we compare TROWARA measurements with a simulation of summer 2012 in Switzerland performed with the Weather Research and Forecasting (WRF) model. It is found that the WRF mod...

The Microwave Emission Model of Layered Snowpacks (MEMLS) was originally developed for microwave emissions of snowpacks in the frequency range 5–100 GHz. It is based on six-flux theory to describe radiative transfer in snow including absorption, 5 multiple volume scattering, radiation trapping due to internal reflection and a combination of coheren...

Results from an experimental campaign, providing measurements of snow microwave backscatter over four winter seasons, are presented. The main dataset consists of tower-based scatterometer observations and coinciding measurements of snow, soil and atmospheric properties. In situ data includes measurements of snow SSA and snow microstructure using co...

Millimeter wave passive imaging systems constitute a good compromise between resolution and penetration depth for a variety of imaging applications. In an outdoor scenario, the cold sky radiation, interacting with the reflectivity characteristics of the targets, constitutes the main source of contrast in the acquired images. In indoor applications...

Original Report from 1989. Publication in English: C. Mätzler, "Microwave transmissivity of a forest canopy: Experiments made with a beech, Remote Sensing of Environment, Vol. 48, pp. 172-180 (1994).

The water budget approach is applied to an atmospheric box above Switzerland (hereafter referred to as the “Swiss box”) to quantify the atmospheric water vapour flux using ECMWF ERA-Interim reanalyses. The results confirm that the water vapour flux through the Swiss box is highly temporally variable, ranging from 1 to 5 · 107 kg/s during settled an...

TEMPERA (TEMPERature RAdiometer) is a new ground-based radiometer which measures in a frequency range from 51–57 GHz radiation emitted by the atmosphere. With this instrument it is possible to measure temperature profiles from ground to about 50 km. This is the first ground-based instrument with the capability to retrieve temperature profiles simul...

ESA's SnowScat instrument is a real aperture scatterometer which was developed by Gamma Remote Sensing AG (CH). It operates in a continuous wave mode, covers a frequency range of 9.15 (X-band) to 17.9 GHz (Ku-band) in a user-defined frequency-step and have a po-larimetric capability. The measurement campaigns were started first in Feb. 2009 at Weis...

Hair-ice is a rather unknown phenomenon. In contrast to generally known frost needles, originating from atmospheric water and expanding e.g. from plant surfaces in all directions, hair ice grows from the basis of wet, rotten hardwood. The hair-like, flexible, linear structures may reach up to 10 cm in length without any ramifications. Hair-ice appe...

The possibility of high-resolution SAR imagery to derive information on the Snow Water Equivalent (SWE) of seasonal snow cover is one of the main goals of the proposed CoReH2O (Cold Regions Hydrology High-Resolution Observatory) mission. CoReH2O is a candidate 7th Earth Explorer Core mission by the European Space Agency (ESA), currently in Phase A....

Soil freezing and thawing, including the winter-time evolution of soil frost, are important characteristics influencing hydrological and climate processes at the regions of seasonal frost and permafrost, which include major land areas of North America and northern Eurasia. Changes in the seasonal behaviour of soil frost have a major effect on the s...

TEMPERA is a new ground-based radiometer which measures in a frequency range from 51-57 GHz radiation emitted by the atmosphere. The instrument operates thermally stabilized inside a lab. With this instrument it is possible to measure temperature profiles from ground to about 50 km. This is the first ground-based instrument with the capability to r...

The daytime summer phenomenon of the mesoscale transport of air and water vapour from the Swiss lowlands into the nearby western Alps, leading to orographic convection, is investigated using a range of independent observations. These observations are: Global Positioning System (GPS) integrated water vapour (IWV) data, the TROWARA microwave radiomet...

Radiative properties at 1.4 GHz of vine vegetation are investigated by measuring brightness temperatures with the ETH L-band Radiometer II (ELBARA II) operated on a tower at the Mediterranean Ecosystem L-band Characterisation Experiment III (MELBEX III) field site in Spain. To this aim, experiments with and without a reflecting foil placed under th...

During summer and autumn 2007, a 11 GHz microwave radiometer was deployed in an experimental tree plantation in Sardinilla, Panama. With this instrument, the opacity of the tree canopy was derived from incoming brightness temperatures received on the ground. A collocated eddy-covariance flux tower measured water vapor fluxes and meteorological vari...

Invited Presentaion

In recent years, several studies have shown that atmospheric aerosols are relevant to climate and population health. One of the most comprehensive variables to remotely assess the aerosol loading in the atmosphere from ground-based measurements is Aerosol Optical Depth (AOD) which measures the magnitude of aerosol extinction (due to scattering and...

A time series of the hemispheric distribution of integrated water vapor (IWV) measured with the All-Sky Multi Wavelength Radiometer is analyzed by means of empirical orthogonal functions (EOFs). The data were acquired in February 2007 at the Zimmerwald Observatory in Switzerland. It is shown that the analysis of temporally demeaned time series yiel...

The Scanning Polarimetric Imaging RAdiometer at 91 GHz with an angular resolution of 0.5° was used to investigate the dynamics of the atmosphere. We introduced a new imaging method by continuously scanning the sky over a range of elevation angles in a fixed azimuth direction. The measurements were realized during three different situations: clear s...

In a combined experimental and model study, we investigated the thermal L-band signatures of a sandy soil with periodic topography (furrows) with dimensions close to the observation wavelength of 21 cm. Measurements were carried out with a radiometer mounted on a tower and aimed at a soil box with an artificially prepared furrowed soil surface. Cor...

During summer and autumn 2007, a 11 GHz microwave radiometer was deployed in an experimental tree plantation in Sardinilla, Panama. The opacity of the tree canopy was derived from incoming brightness temperatures received on the ground. A collocated eddy-covariance flux tower measured water vapor fluxes and meteorological variables above the canopy...

Inversion of tropospheric profiles from ground-based microwavemeasurements requires a simple and accurate model for calculating the brightness temperatures as received by the radiometer. In the first part, an analytic solution of the radiative transfer equation is derived for an exponentially decaying absorption coefficient and a linear temperature...

Integrated water vapour (IWV) is the vertical column density of atmospheric water vapour. IWV can be determined from microwave radiances measured by multi-channel radiometers at ground or in space. Quality and quantity of IWV measurements rapidly increased during the last 10 to 20 years. Global maps and time series of IWV give evidence for a strong...

1] The absorption of liquid clouds was determined in the frequency range from 21 to 31 GHz and over the temperature range from 246 to 279 K. The information was derived from continuous surface‐based microwave and infrared radiometer observations at Bern, Switzerland, from 2006 to 2010 and using satellite data for cloud‐top temperature. The results...

Surface-based microwave studies made in the Austrian Alps during the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/XSAR) experiment in April 1994 are described, and are compared with the SAR data. The SAR test region included glaciers and unglaciated surfaces which were snow covered. Clear differences between these two surface t...

The Scanning Polarimetric Imaging Radiometer (SPIRA) is a passive microwave imaging system operating around 91 GHz. It consists of a two orthogonally polarized receiver channels and an analog adding correlator network with 2 GHz bandwidth, which can measure all four Stokes parameters simultaneously by scanning the scene with an offset parabolic ref...

We investigated the influence of a wire grid above a paved ground on thermal brightness at 1.4 GHz. Reflectivities were derived from dual-polarized brightness temperature measurements for different grid orientations and wire spacings between 2.5 and 20 cm. For spacings larger than a quarter of a wavelength (≈5 cm), the grid had no impact on the obs...

International Geoscience and Remote Sensing Symposium, Honolulu, Hawaii, July 2010 The main goal of ESA’s (European Space Agency) SMOS (Soil Moisture and Ocean Salinity) mission is to deliver global fields of surface soil moisture (SM) and sea surface salinity, with enough resolution to be used in numerical weather prediction and global climate mo...

The COld REgions Hydrology High-resolution Observatory (CoReH20) Mission proposes a dual frequency radar operating at 9.6 and 17 GHz utilizing VV and VH polarization [1]. By combining Xand Ku-Band with both coand cross-polarization diversity it is possible to estimate the Snow Water Equivalent of dry snow. To support this proposed mission, ESA has...

Information on the complex dielectric constant is interesting to determine the penetration depth at a given frequency and thus to explore the potential of ground-penetrating microwave sensors. For a quartz-rich sand from Lake Superior, Ontario, Canada, the complex dielectric constant was measured with a coaxial cavity resonator. Apart from effects...

The Scanning Polarimetric Imaging RAdiometer SPIRA at 91 GHz with an angular resolution of 0.5° was used to investigate the dynamics of the atmosphere. We introduced a new imaging method by continuously scanning the sky over a range of elevation angles in a fixed azimuth direction. The measurements were realized during three different situations: c...

The emission of bare soils at microwave L-band (1-2 GHz) frequencies is known to be correlated with surface soil moisture. Roughness plays an important role in determining soil emissivity although it is not clear which roughness length scales are most relevant. Small-scale (i.e., smaller than the resolution limit) inhomogeneities across the soil su...

L-band (1-2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is...

Calibration of microwave radiometers is a critical task and remains a key issue for the accuracy of brightness-temperature measurements. The tipping-curve calibration method is a well-established technique for ground-based microwave radiometers measuring at frequencies where the opacity of the atmosphere is low. This method relies on the known rela...

An uncooled commercial infrared camera is used to retrieve horizontal winds at cloud-base height. The camera is equipped with a microbolometer array of 320 times 240 pixels covering a field of view of 32deg times 24deg. It operates in the atmospheric window from 7.5 to 14 mum . In this wavelength range, the camera has day and night measurement capa...

Integrated Water vapour (IWV) has been measured since 1994 by the TROWARA microwave radiometer in Bern, Switzerland. Homogenization techniques were used to identify and correct step changes in IWV related to instrument problems. IWV from radiosonde, GPS and sun photometer (SPM) was used in the homogenisation process as well as partial IWV columns b...

Monitoring atmospheric water is essential for the understanding of the dynamic processes of the atmosphere and for the assessment of wave-propagation properties. Microwave radiometers, in combination with a thermal infrared channel, have the potential to fulfill these tasks. This paper is focused on the surface-based system TROWARA with microwave c...

Monitoring microwave attenuation (20 to 45 GHz) of directional transmission links is a method to derive rain rate at high time resolution and in near-real time. Raindrops falling through a propagation path of a microwave link attenuate the transmitted signal quasi linearly with rain rate, allowing the estimation of path-averaged rain intensity. The...

In many cases, the largest uncertainty in synthetic aperture radar interferometry (InSAR) is a range delay caused by the presence of atmospheric water vapour resulting in a phase disturbance. This limits the accuracy of InSAR products such as digital elevation models (DEMs) and terrain subsidence maps. The quality of these products could be dramati...