Electrically Scanning Microwave Radiometer Research Articles

Mapping of sea ice concentration using the NASA NIMBUS 5 Electrically Scanning Microwave Radiometer data from 1972–1977

Abstract. The Electrically Scanning Microwave Radiometer (ESMR) instrument onboard the NIMBUS 5 satellite was a one-channel microwave radiometer that measured the 19.35 GHz horizontally polarized brightness temperature (TB) from 11 December 1972 to 16 May 1977. The original tape archive data in swath projection have recently been made available online by the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC). Even though the ESMR was a predecessor of modern multi-frequency radiometers, there are still parts of modern processing methodologies which can be applied to the data to derive the sea ice extent globally. Here, we have reprocessed the entire dataset using a modern processing methodology that includes the implementation of pre-processing filtering, dynamical tie points, and a radiative transfer model (RTM) together with numerical weather prediction (NWP) for atmospheric correction. We present the one-channel sea ice concentration (SIC) algorithm and the model for computing temporally and spatially varying SIC uncertainty estimates. Post-processing steps include resampling to daily grids, land-spillover correction, the application of climatological masks, the setting of processing flags, and the estimation of sea ice extent, monthly means, and trends. This sea ice dataset derived from the NIMBUS 5 ESMR extends the sea ice record with an important reference from the mid-1970s. To make it easier to perform a consistent analysis of sea ice development over time, the same grid and land mask as used for EUMETSAT's OSI-SAF SMMR-based sea-ice climate data record (CDR) were used for our ESMR dataset. SIC uncertainties were included to further ease comparison to other datasets and time periods. We find that our sea ice extent in the Arctic and Antarctic in the 1970s is generally higher than those available from the National Snow and Ice Data Center (NSIDC) Distributed Active Archive Center (DAAC), which were derived from the same ESMR dataset, with mean differences of 240 000 and 590 000 km2, respectively. When comparing monthly sea ice extents, the largest differences reach up to 2 million km2. Such large differences cannot be explained by the different grids and land masks of the datasets alone and must therefore also result from the differences in data filtering and algorithms, such as the dynamical tie points and atmospheric correction. The new ESMR SIC dataset has been released as part of the ESA Climate Change Initiative (ESA CCI) program and is publicly available at https://doi.org/10.5285/34a15b96f1134d9e95b9e486d74e49cf (Tonboe et al., 2023).

Greenland surface melt trends 1973–2007: Evidence of a large increase in 2007

A time series of surface melt extent, frequency and onset has been updated to include data from Electrically Scanning Microwave Radiometer (ESMR) (1973, 1974 and 1976), Scanning Multichannel Microwave Radiometer (SMMR) (1979–1987) and the Special Sensor Microwave/Imager (SSM/I) (1987–2007). The seasonal melt departure (SMD), the sum from 1 June to 31 August of the departure from average of each day's melt extent, is a new metric used to describe the amount of melt. Results show a large increase in melt in summer 2007, 60% more than the previous high in 1998. During summer 2007, some locations south of 70°N had as many as 50 more days of melt than average. Melt occurred as much as 30 days earlier than average. The SMD is shown to be significantly related to temperatures at coastal meteorological stations, although 2007 had more melt than might be expected based on the summer temperature record.

Interannual variability of monthly Southern Ocean sea ice distributions

The region of the Southern Ocean exhibiting interannual variability in monthly averaged sea ice distributions has been mapped and analyzed using data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) and the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR). Over the 13‐year record from the two instruments (1973–1976 and late 1978 through mid‐1987), interannual variability is particularly high for the early summer month of December, when 10 × 106 km2 of the ocean had ice‐covered conditions in some years and ice‐free conditions in other years. This area of December variability is almost three times the ocean area consistently having ice‐covered conditions in the 13 ESMR/SMMR Decembers. In contrast, in mid‐winter the area of consistent ice coverage far exceeds the area of variability, which, in spite of the much greater ice coverage overall, is not as large as the area of variability in December. The mid‐winter variability is confined to (1) a ring of variable width around the edge of the ice pack and (2) the location of the 1974–1976 Weddell polynya. Separation of the results to the ESMR and SMMR time periods shows that ice in the West Indian Ocean and the Ross Sea tended to be more expansive in the earlier, ESMR years than in the later, SMMR years, but that ice in the Weddell Sea tended to be less expansive in the ESMR years. In the Bellingshausen and Amundsen Seas, the ESMR years tended to have less summer ice than the SMMR years but not less winter ice. The images and plots provide a succinct summary of the range of spatial distributions of Southern Ocean sea ice during the ESMR and SMMR time periods. They can hence be used as a convenient base for comparisons with future sea ice distributions in the effort to identify occurrences of climate change.

NASA sea ice validation program for the Defense Meteorological Satellite Program special sensor microwave imager

The launch of the first Defense Meteorological Satellite Program (DMSP) special sensor microwave imager (SSM/I) on June 19, 1987, was of particular significance to the polar research community in that it extended the series of polar‐orbiting passive microwave imager s which began with the Nimbus 5 electrically scanning microwave radiometer (ESMR) in 1972 and continued until August 1987 with the Nimbus 7 scanning multichannel microwave radiometer (SMMR). Six additional SSM/I instruments will be launched over the next 2 decades as part of the DMSP program.In 1982, in recognition of the importance of the SSM/I to the polar research community, NASA established a program to process, archive, and distribute gridded SSM/I microwave radiances and derived sea ice concentrations for both polar regions. A key element of this effort was the initiation of a sea ice validation program for the purpose of providing the user community a measure of the precision and accuracy of the derived sea ice products. Sea ice remote sensing specialists were invited to serve on the NASA sea ice validation team to define and implement the program [Cavalieri and Swift, 1987]. A parallel program which included other geophysical parameters was established by the Department of Defense under the leadership of J. P. Hollinger at the Naval Research Laboratory [Hollinger, 1989].

Arctic sea ice 1973–1987: Seasonal, regional, and interannual variability

Satellite passive‐microwave data, available for most of the period since 1972, have enabled a global description of the sea ice cover impossible prior to the 1970s. In this paper we analyze sea ice extents in the northern hemisphere over the period 1973–1987, using data derived from the Nimbus 5 electrically scanning microwave radiometer (ESMR) and the Nimbus 7 scanning multichannel microwave radiometer (SMMR). The record shows an average seasonal cycle ranging from a summer minimum of 8.5×106 km2 in September to a winter maximum of 15×106 km2 in March, with considerable interannual variability found both regionally and hemispherically. When yearly averaged sea ice extents are examined for trends, some regions (for example, Baffin Bay/Davis Strait) exhibit upward trends, while other regions (for example, the Kara and Barents seas) exhibit downward trends. The northern hemisphere overall shows no significant trend over the 1973–1987 period, although over the ESMR years (1973–1976) there was an upward trend and over the 8 full SMMR years (1979–1986) there was a lesser downward trend. The record as a whole gives no definitive indication from the varying sea ice extents of any consistent warming or cooling of the north polar region.

Seasonal and Regional Variations of Northern Hemisphere Sea Ice as Illustrated with Satellite Passive-Microwave Data For 1974

A detailed description of the seasonal cycle of Northern Hemisphere sea ice for 1974 is provided by the passive microwave data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR). Sea ice extent has been mapped and analyzed in eight regions of the Arctic and marginal seas. In the seasonal sea ice areas, the ice concentration is also mapped, whereas in areas of first-year and multiyear ice mixtures, the corresponding mapping is of a parameter representing a combination of ice concentration and multiyear ice fraction. The total monthly ice extent increased from a sharp minimum of 7.6 × 106 km2 in September, when the ice pack was mostly confined to the central Arctic Ocean and portions of the Greenland Sea, Kara Sea, and Canadian Archipelago, to a broad maximum of 14.4 × 106 km2 in March, when the ice cover was nearly complete in the Arctic Ocean, Hudson Bay, Kara Sea, and Canadian Archipelago and was extensive for large portions of the other peripheral seas and bays. In the areas of seasonal sea ice coverage, the average ice concentration was approximately 75% in winter, which is close to the values observed in the Southern Ocean and significantly less than the greater-than-95% concentrations observed in the central Arctic Ocean and Hudson Bay, where the ice packs are constrained by land boundaries. Midwinter decreases in ice extent for 1—2 months are noted in the regions of the Greenland Sea and the Kara and Barents Seas.

Seasonal and Regional Variations of Northern Hemisphere Sea Ice as Illustrated with Satellite Passive-Microwave Data For 1974

A detailed description of the seasonal cycle of Northern Hemisphere sea ice for 1974 is provided by the passive microwave data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR). Sea ice extent has been mapped and analyzed in eight regions of the Arctic and marginal seas. In the seasonal sea ice areas, the ice concentration is also mapped, whereas in areas of first-year and multiyear ice mixtures, the corresponding mapping is of a parameter representing a combination of ice concentration and multiyear ice fraction. The total monthly ice extent increased from a sharp minimum of 7.6 × 106 km2 in September, when the ice pack was mostly confined to the central Arctic Ocean and portions of the Greenland Sea, Kara Sea, and Canadian Archipelago, to a broad maximum of 14.4 × 106 km2 in March, when the ice cover was nearly complete in the Arctic Ocean, Hudson Bay, Kara Sea, and Canadian Archipelago and was extensive for large portions of the other peripheral seas and bays. In the areas of seasonal sea ice coverage, the average ice concentration was approximately 75% in winter, which is close to the values observed in the Southern Ocean and significantly less than the greater-than-95% concentrations observed in the central Arctic Ocean and Hudson Bay, where the ice packs are constrained by land boundaries. Midwinter decreases in ice extent for 1—2 months are noted in the regions of the Greenland Sea and the Kara and Barents Seas.

Large‐scale short‐period sea ice atmosphere interaction

Changes in the microwave brightness temperature measured by the Electrically Scanning Microwave Radiometer (ESMR) flown on board the Nimbus V satellite reveal large‐scale sea ice fluctuations in the Antarctic marginal ice zone. These ice margin fluctuations are predominantly wave numbers 1–4, with phase speeds of about 3 m/s independent of wave number. The spatial pattern and eastward advection of the sea ice anomalies match those of the atmospheric sea level pressure, and are consistent with sea ice displacement due to surface wind stress. Examination of the outgoing longwave radiation indicates that suppression of high clouds in regions of increased sea ice increases the radiative cooling which contributes to maintaining the ice. Data from three winter seasons indicate about a one‐third probability of occurence of this large scale high frequency sea ice atmosphere interaction during any given 2‐week period in winter.

Synoptic sea ice‐atmosphere interactions in the Chukchi and Beaufort Seas from NIMBUS 5 ESMR data

Three case studies are used to evaluate the interactions between individual synoptic events and the sea ice cover of parts of the western Arctic in October 1976. Changes in both ice extent and concentration are assessed quantitatively by using 2‐day averaged passive microwave data from the NIMBUS 5 ESMR (electrically scanning microwave radiometer). These are related to daily 850‐mbar resultant wind patterns for the periods considered. Strong anticyclonic conditions are associated with relatively static surface brightness temperatures (TB) and hence with generally stable ice conditions. Conversely, a quasi‐stationary cyclonic system produces marked TB variations involving rapid changes in ice edge position and ice concentrations. Transient atmospheric (temperature, moisture) fluctuations, associated with the passage of synoptic systems, are found not to be negligible in the interpretation of microwave sea ice TB signatures on short time scales.

Atmosphere ‐ sea ice interactions in the Beaufort/Chukchi Sea and in the European sector of the Arctic

Electrically Scanning Microwave Radiometer (ESMR) data for ‘winter’ months, November 1973 to April 1974, and for ‘summer’, May to October 1974, are used to examine the synoptic scale sea ice‐atmosphere interactions over the Beaufort/Chukchi Sea and the European sector of the Arctic. The synoptic scale variability in the microwave brightness temperatures and sea level atmospheric pressure and temperature is examined through the use of principal components analysis. Changes occurring in the ice ablation season are found to be responsible for much of the variance in the data. Canonical correlations are used to derive the leads and lags in the ice‐atmosphere system. Positive feedbacks are identified between the ice and the atmosphere, and the direction of the ice‐atmosphere forcing is found to vary both seasonally and regionally, and also between the areas of permanent pack and the seasonal sea ice zone.

On the seasonal sea ice cover of the Sea of Okhotsk

Free of ice 4 months of the year, the Sea of Okhotsk begins to freeze over in a few coastal locations in November, attains its maximum ice coverage usually in mid March, and by June retains ice in only a few coastal regions. This sequence is well recorded by satellite imagery from the Electrically Scanning Microwave Radiometer (ESMR) on board Nimbus 5. Four years of ESMR data reveal significant interannual variations in the maximum ice cover and in the smoothness of the growth and retreat periods. Of the years 1973–1976, the heaviest ice cover occurred in 1973, and the growth period most interrupted by temporary ice edge retreats was in 1974. Comparison of the general features of the cycle of sea ice distribution with basic oceanographic factors shows that ice forms first in cold, shallow, low‐salinity waters and then seems to drift in a direction approximating the Okhotsk‐Kuril current system. Two basic patterns of ice edge positioning which occur frequently in the ESMR data are identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns. Certain major interannual variations in the ice extents are accounted for by interannual contrasts in the atmospheric pressure fields.

Antarctic sea ice concentrations inferred from Nimbus 5 ESMR and Landsat imagery

A quantitative comparison is made of Antarctic sea ice concentration derived from the Nimbus 5 electrically scanning microwave radiometer (ESMR) and from the Landsat 1 and Landsat 2 MSS‐7 near‐infrared band images. The set of images includes regions near the ice edge and near the continental boundary during late winter or spring. The ice‐covered areas in the southern ocean exhibit microwave brightness temperature predominantly characteristic of first‐year sea ice with emissivity of 0.92. The percentage ice cover is derived from the microwave data, using an algorithm that uses this emissivity and interpolated climatological physical temperatures and that is not dependent on spatial resolution. Classification of ice floes and open water in cloud‐free Landsat images provides an alternative determination of large‐scale ice concentrations, but the limitations of this method are shown. In various areas, especially near the ice edge, Landsat data are limited in their ability to resolve individual ice floes. A classification procedure for Landsat data based on a threshold radiance level for water overestimates the ice concentration because this method tends to classify mixtures of open water and unresolved ice floes as fully ice covered. A proportional classification based on observed reflectance gives better agreement with the ESMR ice concentration values because it does not require that each open water area be resolved in the Landsat imagery. The derived ice concentrations from the ESMR and Landsat data, using the proportional classification method, agree to ±15%, with the largest uncertainties occurring in regions of low concentration.

Analysis of atmosphere-sea ice interactions in the Arctic Basin using ESMR microwave data†

Abstract Data from the Electrically Scanning Microwave Radiometer (ESMR) on NIMBUS-5 are used to determine the spatial and temporal patterns of change in microwave brightness signatures of Arctic sea ice during a full annual cycle (1973/74). Interactions of ice conditions with the atmosphere are examined using grid point data for surface air temperature and atmospheric pressure. Principal components analysis is used to examine the major elements present in the microwave and atmospheric data. Component scores from these analyses are then used in a canonical correlation analysis to determine interassociations present between the ice and atmosphere in the Beaufort Sea and the European sectors on a synoptic time scale. The synoptic weather conditions associated with the pattern of snow melt on the ice in spring 1974 are described, and a clarification of possible alternative interpretations of features identified as polynyi occurring at 80-85° N. during the late summer 1974 is presented.

New Features of Global Climatology Revealed by Satellite-Derived Oceanic Rainfall Maps

Quantitative rainfall maps over the oceanic areas of the globe were derived from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) data. Analysis of satellite derived oceanic rainfall maps reveal certain distinctive characteristics of global patterns for the years 1973-74. The main ones are (1) the forking of the Intertropical Convergence Zone in the Pacific, (2) a previously unrecognized rain area in the South Atlantic, (3) the bimodal behavior of rainbelts in the Indian Ocean and (4) the large interannual variability in oceanic rainfall. These features are discussed.

Satellite-Observed Latent Heat Release in a Tropical Cyclone

Data from the Nimbus 5 electrically scanning microwave radiometer (ESMR) are used to make calculations of the latent heat release (L.H.R.) and the distribution of rainfall rate in a tropical cyclone as it grows from a tropical disturbance to a typhoon. The L.H.R. (calculated over a circular area of 4 deg latitude radius) increases during the development and intensification of the storm from a magnitude of 2.7 X 10 to the 21st power ergs/s (in the disturbance stage) to 8.8 X 10 to the 21st power ergs (typhoon stage). The latter value corresponds to a mean rainfall rate of 2.0 mm hr/s. The more intense the cyclone and the greater the L.H.R., the greater the percentage contribution of the larger rainfall rates to the L.H.R. In the disturbance stage the percentage contribution of rainfall rates less than or minus 6 mm hr/s is typically 8%; for the typhoon stage, the value is 38%. The distribution of rainfall rate as a function of radial distance from the center indicates that as the cyclone intensifies, the higher rainfall rates tend to concentrate toward the center of the circulation.

Passive microwave images of the polar regions and research applications

Passive microwave images of the polar regions, first produced after the launch of the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR)in December 1972, have become a valuable new source of polar information. Some of the potential applications of this new capability were anticipated. Of these, the sensing of sea ice through clouds and the polar night is probably the most important application for polar research and for operations on the polar seas. Other applications, such as the measurement of certain near-surfaceice sheet parameters, have been formulated more recently. Measurement of various ocean surface parameters is expected from the forthcoming multifrequency microwave observations. Undoubtedly additional uses of passive microwave datawill be conceived and developed. Two remarkable aspects of satellite-borne microwave radiometers are the complete spatial detail obtained by the scanning sensors and the temporal detail provided by continual coverage. For example, the observations of detailed microwave emission patterns over the Antarctic ice sheet should yield information that could not be obtained by surface or even aircraft measurements. Sequences of images produced at three-day intervalsreveal short-term ice sheet and sea ice phenomena that would otherwise be missed.

Satellite microwave observations of the Utah Great Salt Lake Desert

Microwave data acquired over the Great Salt Lake Desert area by sensors aboard Skylab and Nimbus 5 indicate that the microwave emission and backscatter were strongly influenced by contributions from subsurface layers of sediment saturated with brine. This phenomenon was observedby Skylab's S‐194 radiometer operating at 1.4 GHz, S‐193 RADSCAT (Radiometer‐Scatterometer) operating at 13.9 GHz, and the Nimbus 5 ESMR (Electrically Scanning Microwave Radiometer) operating at 19.35 GHz. The availability of ESMR data over an 18‐month period allowed an investigation of temporal variations.

Tropical Cyclone Rainfall as Measured By the Nimbus Electrically Scanning Microwave Radiometer

Abstract A selected group of 1973 North Pacific Ocean tropical cyclones was studied by using data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR), the Temperature-Humidity Infrared Radiometer (THIR), NOAA-2 and USAF DMSP imageries. From the unique combination of infrared, visible, and microwave data, it was possible during various stages of storm development to differentiate between dense cirrus outflow and rain areas, to identify centers of circulation and areas of low-level moisture, and by the use of a theoretical model to estimate semi-quantitatively areas of light, moderate, and heavy rainfall rates.