NASA Sea Ice Validation Program for the Defense Meteorological Satellite Program Special Sensor Microwave Imager

The history of the program is described along with the SSM/I sensor, including its calibration and geolocation correction procedures used by NASA, SSM/I data flow, and the NASA program to distribute polar gridded SSM/I radiances and sea ice concentrations (SIC) on CD-ROMs. Following a discussion of the NASA algorithm used to convert SSM/I radiances to SICs, results of 95 SSM/I-MSS Landsat IC comparisons for regions in both the Arctic and the Antarctic are presented. The Landsat comparisons show that the overall algorithm accuracy under winter conditions is 7 pct. on average with 4 pct. negative bias. Next, high resolution active and passive microwave image mosaics from coordinated NASA and Navy aircraft underflights over regions of the Beaufort and Chukchi seas in March 1988 were used to show that the algorithm multiyear IC accuracy is 11 pct. on average with a positive bias of 12 pct. Ice edge crossings of the Bering Sea by the NASA DC-8 aircraft were used to show that the SSM/I 15 pct. ice concentration contour corresponds best to the location of the initial bands at the ice edge. Finally, a summary of results and recommendations for improving the SIC retrievals from spaceborne radiometers are provided

Characterizing maritime trade-wind convection using the HALO Microwave Package (HAMP)

This thesis explores the marine trade-wind convection and the clouds forming within by using spatial-high-resolution airborne remote sensing observations taken from the German High Altitude and LOng range research aircraft (HALO). The nadir-pointing HALO Microwave Package (HAMP) is the central tool of this thesis. HAMP comprises a cloud radar and a 26-channel microwave radiometer (MWR, 22–183 GHz), for which the atmosphere and clouds are semitransparent. The shallow cumulus clouds, like they regularly occur in the trade-wind region, are of particular interest for better understanding the climate. Several studies (e.g., Bony and Dufresne, 2005; Schneider et al., 2017) identified such clouds as a main source of model spread in climate projections. The challenge of this kind of ubiquitous clouds in the models is partly due to large spread in global observations which can be related to the small scale of shallow cumuli and the coarse-scale observations from satellites. This thesis combines three studies around HAMP from the characterization of the HAMP MWR, over the development of MWR retrievals for liquid clouds to the application by evaluating two cloud-resolving simulations. The HAMP MWR is characterized by investigating the random noise of each channel, the covariance within each of the five frequency bands, the brightness temperature (BT) offset, the offset stability, and by suggesting an offset correction. The offset and stability of the HAMP BT acquisitions are studied by comparing the measured BTs to synthetic measurements based on forward-simulated dropsondes. Offsets between −11 and +6 K show a spectral dependency, which repeatedly appears but is shifted between flights. The offsets are most likely caused by uncertainties in the calibration method and changing environmental conditions of the MWR in the belly pod during take-off and ascending. However, an offset correction based on the dropsondes can be developed for each channel as a function of the flight. To better interpret the HAMP BT observations, novel retrievals are developed based on a realistic database of synthetic measurements and corresponding atmospheric profiles. Retrievals of the liquid water path (LWP), rainwater path (RWP), and integrated water vapor (IWV) are developed to describe the clouds and their environment. The retrieved IWV using the offset-corrected BTs agrees with coincident dropsondes and water vapor lidar measurements by 1.4 kg/m² . The theoretical assessment of LWP shows that the LWP error is below 20 g/m² for LWP below 100 g/m² . The absolute LWP error increases with increasing LWP, but the relative error decreases from 20 % at 100 g/m² to 10 % at 500 g/m². The RWP retrieval, which uses the radar in addition to the MWR, can reliably detect RWP larger than 10 g/m² with a Gilbert skill score > 0.75. The retrieval results are summarized in a comparison of the clouds and their moisture environment in the two tropical seasons, which are represented by the field experiments in December 2013 (dry season) and in August 2016 (wet season). Clouds were more frequent, and their average LWP and RWP were higher in the dry season than in the wet season. However, deeper convection with the formation of large frozen particles was less frequent in the dry season. It is hypothesized, that the lower degree of cloud organization in the dry season led to smaller systems with more overall cloud cover. The higher degree of randomness in the dry season comes along with less extremes and is reflected by a narrower distribution of IWV. The variability between (especially the wet-season) flights shows, how statistics from airborne campaigns are affected by the choice of the individual flight pattern. The more homogeneous and cloudy statistics of the dry season are used to assess the representation of shallow cumulus convection and the cloud formation over the ocean in two cloud-resolving simulations generated with the ICON model. The HAMP radar and a backscatter lidar are used for detecting cloud top height (CTH), base height, and precipitation, and the MWR stratifies the cases by LWP. Forward simulators are used to derive the same measurements synthetically from the model data while applying the same instrument-specific cloud-detection thresholds. The analysis reveals a bimodal structure of the CTH. The lower mode relates to boundary layer driven clouds, while the upper mode is driven by moist shallow convection, trapped under the trade inversion at about 2.3 km above sea level. The storm-resolving model (SRM) with 1.25 km horizontal grid spacing resolves the two cloud layers to a limited extend. Most CTHs in the SRM are above the observed lower CTH mode, and top height increases with LWP. The second model with a 300 m grid (large-eddy model, LEM) represents better the observed bimodal distribution of CTH. However, the microphysical schema of neither model can produce in-cloud drizzle-sized particles that were often observed by the radar. This application study shows, how HAMP on HALO provides insightful data to help closing the uncertainty in the models, if interpreted thoroughly

Millimeter wavelength spectroscopy and continuum studies of the planets

Careful observations were made at 86.1 GHz to derive the absolute brightness temperatures of the Sun (7914 + or - 192 K), Venus (357.5 + or - 13.1 K), Jupiter (179.4 + or - 4.7K), and Saturn (153.4 + or - 4.8 K) with a standard error of about 3%. This is a significant improvement in accuracy over previous results. A stable transmitter and novel superheterodyne receiver were constructed and used to determine the effective collecting area of the MWO 4.9 m antenna relative to a previously calibrated standard gain horn. The thermal scale was set by calibrating the radiometer with carefully constructed and tested hot and cold loads. The brightness temperatures may be used to establish an absolute calibration scale and to determine the antenna aperture and beam efficiencies of other radio telescopes at 3.5 mm wavelength

SMMR Simulator radiative transfer calibration model. 2: Algorithm development

Passive microwave measurements performed from Earth orbit can be used to provide global data on a wide range of geophysical and meteorological phenomena. A Scanning Multichannel Microwave Radiometer (SMMR) is being flown on the Nimbus-G satellite. The SMMR Simulator duplicates the frequency bands utilized in the spacecraft instruments through an amalgamate of radiometer systems. The algorithm developed utilizes data from the fall 1978 NASA CV-990 Nimbus-G underflight test series and subsequent laboratory testing

The development of a stepped frequency microwave radiometer and its application to remote sensing of the Earth

The design, development, application, and capabilities of a variable frequency microwave radiometer are described. This radiometer demonstrated the versatility, accuracy, and stability required to provide contributions to the geophysical understanding of ocean and ice processes. A closed-loop feedback method was used, whereby noise pulses were added to the received electromagnetic radiation to achieve a null balance in a Dicke switched radiometer. Stability was achieved through the use of a constant temperature enclosure around the low loss microwave front end. The Dicke reference temperature was maintained to an absolute accuracy of 0.1 K using a closed-loop proportional temperature controller. A microprocessor based digital controller operates the radiometer and records the data on computer compatible tapes. This radiometer exhibits an absolute accuracy of better than 0.5 K when the sensitivity is 0.1 K. The sensitivity varies between 0.0125 K and 1.25 K depending upon the bandwidth and integration time selected by the digital controller. Remote sensing experiments were conducted from an aircraft platform and the first radiometeric mapping of an ocean polar front; exploratory experiments to measure the thickness of lake ice; first discrimination between first year and multiyear ice below 10 GHz; and the first known measurements of frequency sensitive characteristics of sea ice

Review of the CALIMAS Team Contributions to European Space Agency's Soil Moisture and Ocean Salinity Mission Calibration and Validation

Camps, Adriano ... et al.-- 38 pages, 22 figuresThis work summarizes the activities carried out by the SMOS (Soil Moisture and Ocean Salinity) Barcelona Expert Center (SMOS-BEC) team in conjunction with the CIALE/Universidad de Salamanca team, within the framework of the European Space Agency (ESA) CALIMAS project in preparation for the SMOS mission and during its first year of operation. Under these activities several studies were performed, ranging from Level 1 (calibration and image reconstruction) to Level 4 (land pixel disaggregation techniques, by means of data fusion with higher resolution data from optical/infrared sensors). Validation of SMOS salinity products by means of surface drifters developed ad-hoc, and soil moisture products over the REMEDHUS site (Zamora, Spain) are also presented. Results of other preparatory activities carried out to improve the performance of eventual SMOS follow-on missions are presented, including GNSS-R to infer the sea state correction needed for improved ocean salinity retrievals and land surface parameters. Results from CALIMAS show a satisfactory performance of the MIRAS instrument, the accuracy and efficiency of the algorithms implemented in the ground data processors, and explore the limits of spatial resolution of soil moisture products using data fusion, as well as the feasibility of GNSS-R techniques for sea state determination and soil moisture monitoringThis work has been performed under research grants TEC2005-06863-C02-01/TCM, ESP2005-06823-C05, ESP2007-65667-C04, AYA2008-05906-C02-01/ESP and AYA2010-22062-C05 from the Spanish Ministry of Science and Innovation, and a EURYI 2004 award from the European Science FoundationPeer Reviewe

A Roughness Correction for Aquarius Ocean Brightness Temperature Using the CONAE MicroWave Radiometer

Aquarius/SAC-D is a joint NASA/CONAE (Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using an L-band radiometer that measures ocean brightness temperature (Tb). The application of L-band radiometry to retrieve SSS is a difficult task, and therefore, precise Tb corrections are necessary to obtain accurate measurements. One of the major error sources is the effect of ocean roughness that warms the ocean Tb. The Aquarius (AQ) instrument (L-band radiometer/scatterometer) baseline approach uses the radar scatterometer to provide this ocean roughness correction, through the correlation of radar backscatter with the excess ocean emissivity. In contrast, this dissertation develops an ocean roughness correction for AQ measurements using the MicroWave Radiometer (MWR) instrument Tb measurements at Ka-band to remove the errors that are caused by ocean wind speed and direction. The new ocean emissivity radiative transfer model was tuned using one year (2012) of on-orbit combined data from the MWR and the AQ instruments that are collocated in space and time. The roughness correction in this paper is a theoretical Radiative Transfer Model (RTM) driven by numerical weather forecast model surface winds, combined with ancillary satellite data from WindSat and SSMIS, and environmental parameters from NCEP. This RTM provides an alternative approach for estimating the scatterometer-derived roughness correction, which is independent. The theoretical basis of the algorithm is described and results are compared with the AQ baseline scatterometer method. Also results are presented for a comparison of AQ SSS retrievals using both roughness corrections

The Development of a Stepped Frequency Microwave Radiometer and Its Application to Remote Sensing of the Earth

The design, development, application, and capabilities of a variable frequency microwave radiometer are described. This radiometer has demonstrated the versatility, accuracy, and stability required to provide contributions to the geophysical understanding of ocean and ice processes. The design technique utilized a closed-loop feedback method, whereby noise pulses were added to the received electromagnetic radiation to achieve a null balance in a Dicke switched radiometer. Stability was achieved through the use of a constant temperature enclosure around the low loss microwave front end. The Dicke reference temperature was maintained to an absolute accuracy of 0.1 K using a closed-loop proportional temperature controller. Versatility was achieved by developing a microprocessor based digital controller which operates the radiometer and records the data on computer compatible tapes. Accuracy analysis has shown that this radiometer exhibits an absolute accuracy of better than 0.5 K when the sensitivity is 0.1 K. The sensitivity varies between 0.0125 K and 1.25 K depending upon the bandwidth and integration time selected by the digital controller. Computational techniques were developd to (1) predict the radiometric brightness temperature at the input to the radiometer antenna as a function of the geophysical parameters, (2) compute the required input radiometric brightness temperature as a function of the radiometer output using a mathematical model of the radiometer, (3) achieve computational efficiency through a simplified algorithm to determine the expected radiometric brightness temperature, and (4) calculate the emissivity of a layered dielectric media such as ice over water. The effects of atmospheric absorption due to oxygen, water vapor, nonprecipitating clouds have been included. Correction factors for the finite antenna beamwidth, surface roughness, and wind induced foam were employed in these computations. Remote sensing experiments were conducted from an aircraft platform using this radiometer. The purpose of these experiments was to demonstrate that the accuracy and versatility of this instrument had been achieved in actual field experiments. Four significant scientific observations were accomplished during these experiments. These observations consisted of the first radiometric mapping of an ocean polar front, exploratory experiments to measure the thickness of lake ice, first discrimination between first year and multiyear ice below 10 GHz, and the first known measurements of frequency sensitive characteristics of sea ice