THE B-21 CRYPTOGRAPH

ABSTRACT

The acquisition and exploitation of material found on the German cruiser Magdeburg played a major part in the early success at sea enjoyed by the Allied Powers in World War I. The Russian role in this effort, however, has been largely unknown or ignored, at least in English language publications. From the very beginning, the Russians played a major and on-going role, both in the cryptanalytic exploitation effort of the Magdeburg material and in the effective use of this communications intelligence by naval commanders of the Baltic Sea Fleet. The Russians continued to play an active role in this effort throughout the war.     

From the Archives: Polish Interwar MFA's Cipher Compromised?

Abstract

A 1940 report suggests that the cryptosystem used by the interbellum Polish Ministry of Foreign Affairs had been compromised, enabling the Germans to read the encrypted diplomatic traffic of the Poles and learn about their plans in advance.     

Modelling of radar backscattering from low-salinity ice with ice ridges

Abstract

Radar backscattering from a snow-free ice surface characterized by an exponential correlation function is studied for conditions typical in the Baltic Sea. The C-band backscattering coefficient from first-year ice is normally found to be characterized primarily by the air-ice surface roughness. However, if the salinity and temperature are low, as in the Baltic Sea, both volume scattering and ice-water surface scattering might contribute. Even more important than scattering from the level ice is scattering from the ice ridges, and a simple approach is taken to characterize the properties of ice ridges and the corresponding scattering.     

The Bothnian Experiment in Preparation for ERS-1, 1988 BEPERS-88) — an overview

Abstract

BEPERS-88 was an extensive field campaign on the use of Synthetic Aperture Radar (SAR) in sea ice remote sensing in the Baltic Sea. This experiment was performed in order to study the possibilities of using the ERS-1 satellite SAR (and radar altimeter) in connection with the brackish ice in the Baltic Sea. The Canada Centre for Remote Sensing CV-580 C/X-band SAR was flown and an extensive validation programme was carried out. The data have been used for SAR image analysis, backscatter investigations, geophysical validation of SAR over sea ice, and evaluation of the potentials of SAR in operational ice information services. The results indicate that SAR can be used to discriminate between ice and open water, classify ice types into thrcc categories, quantify ice ridging intensity, and determine the ice drift. As an operational tool SAR is expected to be an excellent complement to NOAA imagery and ground truth.     

THE UNSOLVED MESSAGES OF PEARL HARBOR

In 1941, the United States Navy intercepted enough Japanese naval messages to predict the attack on Pearl Harbor if the code which protected them had been solved. The messages would have disclosed that, while the Japanese government cynically conducted diplomatic negotiations with the United States, the Japanese Combined Fleet under Admiral Isoroku Yamamoto, beginning as early as September 1941, systematically prepared ships, crews, weapons, tactics, and a complicated fuel supply system for the most ambitious operation ever undertaken by the Japanese navy. Details of Japan's intentions were hidden from Navy cryptanalysts because of limited manpower resources and because all Japanese navy codes were assigned a lower priority than Japanese diplomatic codes and German submarine threat.     

Comparative experimental study on the use of original and compressed multispectral Landsat data for applied research

Abstract

Parts of two multispectral Landsat scenes, compressed by ratio 6·4/1, were investigated on the effect of the compression on the image contents. Landsat images of the Bayuda desert in Sudan and the Baltic Sea have been submitted to supervised maximum likelihood classification. Partitioning of classified images is given on a percentage basis as a function of sigma. Three-dimensional clusters of spectral channels and histograms show the influence of compression. Discussion of results shows effect of compression on partitioning of classified scenes, being displayed in several tables and figures.     

HOW OP-20-G GOT RID OF JOE ROCHEFORT

ABSTRACT

In late October 1942, LtCmdr Joseph Rocherfort, USN, was dismissed from his job as officer in charge of the Navy's radio intelligence center in Honolulu. Trained in both Japanese language and radio intelligence, he had been sent there a little over a year before by OP-20-G, the element in naval communications in overall charge of radio intelligence. During that time he had seen his beloved Pacific Fleet in both defeat and victory. His contributions in radio intelligence in that short time were legendary among his colleagues in Hawaii and his services were so highly valued by the Commander in Chief of the Pacific Fleet, Admiral Chester Nimitz, that, after the American victory at Midway, he was recommended for a Distinguished Service Medal. This article describes how and why, so early in the war, this multi-talented naval officer lost his job in Hawaii and spent virtually the entire war outside the intelligence field altogether.     

Preliminary results for SeaWiFS vicarious calibration coefficients in the Baltic Sea

The technique of vicarious calibration is used in connection with an atmospheric correction to improve the Sea viewing Wide Field of view Sensor (SeaWiFS) normalized water-leaving radiance by the first determination of mean vicarious calibration coefficients from in situ measurements in the Baltic Sea. A necessary adjustment of the SeaWiFS pre-flight calibration slope was found to be +3.5%, +0.3%, ?1.7%, ?0.4%, +0.8% and ?1.3% for the first six SeaWiFS channels. The derived mean vicarious calibration coefficients are higher than the coefficients in the standard SeaWiFS Data Analysis System (SeaDAS) software but with similar shape and good agreement with other research results. The coefficients were used to obtain better normalized water-leaving radiance from SeaWiFS measurements in the Baltic Sea. The deviations of calculated to measured radiances in the open Baltic Sea are between 3% and 47% in the channels 412 to 670?nm, with the trend of higher deviations in the blue channels. The objective of radiance determination in all SeaWiFS channels with a maximum uncertainty of 5% in clear water regions is probably not reachable in the turbid water of the Baltic Sea.     

Relationship between the attenuation of downwelling irradiance at 490 nm with the attenuation of PAR (400 nm-700 nm) in the Baltic Sea

The vertical attenuation coefficient of diffuse downwelling irradiance at 490 nm (K_d 490) is a parameter that we routinely derive from SeaWiFS images of the Baltic Sea. Here, through model simulations, we examine the relationship between K_d(490), and the vertical attenuation coefficient of PAR (K_d PAR), as this later coefficient determines the light available for aquatic photosynthesis. A simple semi-analytical model is used to predict K_d(490) and K_d(PAR), as a function of the concentrations of chlorophyll, colored dissolved organic material (CDOM), suspended inorganic, and suspended organic particulate material. A series of model simulations based on variations in these optically significant constituents over a range realistic for the Baltic Sea, are used to define the relationship between the two attenuation coefficients.

Kd(PAR)=0.6677Kd^0.6763(490).     

Sea surface temperature simulation and forecast

Unconventional computing of sea surface temperature (SST) was once featured by NASA as a unique merger of science and art. Our approach led to a discovery that just one geographical point could be sufficient to track global anomalies of SST based on El Niño Southern Oscillation (ENSO). Such single point in the Pacific Ocean off of the island of Isabella in the Galapagos Islands was named the Galapagos indicator. Now we show that a single point in the Baltic Sea off of the coast of Göteborg could be also sufficient to track ENSO. We propose to name it the Baltic indicator. We also demonstrate that two crisis falls of oil price in 2008 and 2014 followed just after the local maximums of Baltic indicator. However, Baltic and Galapagos indicators do not show any evident trend in settling the global warming from the beginning of this century.     

Applicability of SAR-based wave retrieval for wind–wave interaction analysis in the fetch-limited Baltic

In this article, a method for the detection of wave field parameters from synthetic aperture radar (SAR) imagery in the fetch-limited Baltic Sea is presented. Over the Baltic Sea region, common southwest (SW) and west (W) winds induce steep waves with shorter wavelengths compared with ocean waves. Thus, with the use of previous SAR sensors (e.g. ENVISAT/ASAR), it was not possible to detect individual waves and retrieve image wave number spectra. Since the year 2007, when TerraSAR-X (TS-X) reached its orbit, high spatial resolution data is available for measuring the sea-state parameters: the individual waves up to 30 m wavelength and their refraction can be distinguished. The main objective of this work was to demonstrate the capability of detecting wave field parameter from (TS-X) imagery in the Baltic Sea. The wave field parameters obtained from the SAR imagery were compared with in situ measurements and the Simulating WAves Nearshore (SWAN) wave model. The comparison of SAR-based wave field information with buoy measurements showed high agreement in case of wave propagation direction (r = 0.95) and wavelength (r = 0.83). A significant correlation is also seen between SWAN- and SAR-derived wave propagation direction (r = 0.87) and wavelengths (r = 0.91). With the case studies, it is shown that SAR data enables one to detect land shadow effects and small-scale wave field variations in the coastal zone. It was shown that SAR data is also valuable for improving and interpreting the wave model results. In consequence of common slanting fetch cases over the Baltic Sea region, it was demonstrated that the peak wave directions differ from the mean wind directions up to 43°.     

THE MARKET FOR ENCRYPTION

Abstract

In 1942, the United States Navy recognized that in the ranks of newly-enlisted WAVES lay the potential for much-needed assistance in processing German Navy Enigma messages that had been intercepted and deciphered. This is the improbable story of one of those WAVES.     

The relation between SAR imagery and regional sea ice ridging characteristics from BEPERS-88

Abstract

In the Bothnian Experiment in Preparation for ERS-1 (BEPERS-88) airborne laser profiles and Synthetic Aperture Radar (SAR) images were obtained simultaneously over the pack ice in the Bay of Bothnia, Baltic Sea. The possibility of mapping ice ridging characteristics using SAR has been analysed. SAR intensity histograms and ridging statistics have been compared in regions with length scales from 3 to 23 km. The measures for the intensity of ridging were taken from the profilometer data as functions of the number of ridges and mean ridge height. The results show that, from SAR intensity distribution, an average of 10 per cent upper tail divided by the overall average is a good predictor for the ridging intensity. This predictor explains 80-90 per cent of the variance.     

SeaWiFS data analysis and match-ups with in situ chlorophyll concentrations in Danish waters

For the year 1999 all Sea viewing Wide Field of view Sensor (SeaWiFS) scenes of the Danish waters from the North Sea to the Baltic Sea were browsed, and a total of 47 SeaWiFS scenes with reasonably low cloud cover and, therefore, potential in situ match-ups were found and processed. The in situ data used as match-ups were collected on routine monitoring cruises by Danish and Swedish environmental authorities. A few stations in the North Sea, Skagerak and the western Baltic Sea were sampled, while most stations were located in Kattegat and the inner Danish waters. A turbid water SeaWiFS atmospheric correction algorithm was applied, since the standard SeaWiFS algorithm for chlorophyll-a (CHL) has been shown to be fairly inaccurate in turbid coastal waters. This is due to both inaccurate atmospheric and to relatively high and variable abundance of yellow substance. The application of the turbid atmospheric correction substantially improved the SeaWiFS CHL estimates. Regressions between SeaWiFS estimates using the OC2 and OC4 algorithms used in the SeaDAS software (versions 3.3 and 4.0, respectively) and in situ CHL values were made as well, and regression with a number of other possible reflectance ratios with SeaWiFS channels. The best correlation was found to be R²=0.54 using a double-ratio algorithm using both R510/R555 and R443/R670, while the OC4v4 had the second best correlation of R²=0.39. Among other single ratios, the R510/R555 had the highest correlation with CHL, which was expected since this is also the ratio that OC4v4 most often switches to in the waters investigated here. The range of CHL concentrations in this study was rather limited (all but three points from 0.5–3?mg?m^?3) so there is a need for inclusion of more data to expand the concentration range. This should be possible using also data from 2000, 2001 and onwards and, hereafter, a more ‘stable’ empirical algorithm can be derived for the Danish waters.     

Work demands and need for recovery from work in ageing seafarers

This study was conducted on a population of seafarers serving in the Royal Fleet Auxiliary (RFA), the organisation providing support at sea to the Royal Navy. An investigation into work-related fatigue in RFA personnel onboard ships was carried out following changes to the regulations concerning maximum retirement age, to determine whether age was associated with recovery from work demands. A total of 322 personnel aged from 19 to 61 years were interviewed onboard seven RFA ships. The Need for Recovery scale was used to measure fatigue and work demands exposure was measured using the Baecke questionnaire and the NASA Task Load Index. It was found that older personnel did not have higher work-related fatigue than younger personnel. A measure of frustration at work was found to be most strongly related to work-related fatigue, even in seafarers who carried out physically demanding jobs. Work-related fatigue was found to accumulate over time in personnel who continued to be exposed to work demands onboard a ship. Finally, a relatively high level of work-related fatigue was found in the RFA sample as a whole, which may hold implications for management interventions. It was concluded that older personnel in the RFA can cope with the day-to-day demands of working life as well as younger personnel, possibly due to a ‘survivor effect’, whereby those personnel who do not cope as well with work demands leave and find a different job, leaving only those who successfully deal with the demands of working life at sea.

Statement of Relevance: In order to manage work demands in seafarers, it is important to identify the most fatiguing demands. Age is of interest because of the demographic ageing of the workforce. Age was not associated with a higher need for recovery. Psychological work demands had a greater effect on need for recovery than physical work demands.     

Correlation of precipitation estimates from spaceborne passive microwave sensors and weather radar imagery for BALTEX PIDCAP

This paper describes the evaluation of a combined radar and passive microwave dataset obtained during the PIDCAP study of the Baltic Sea Experiment (BALTEX), where three-dimensional volumes of data from the Gotland radar were obtained timed according to the overpasses of the DMSP-satellites F10 and F13. Both satellites are equipped with a Special Sensor Microwave/Imager (SSM/I), suitable for precipitation retrievals. We compare radar precipitation estimates, convolved to the native resolution of the SSM/I, at different altitudes with polarization and scattering indices ( S 85 ) derived from the SSM/I. For all 22 overpasses investigated here radar precipitation estimates at 3-4 km altitude correlate well with the SSM/I-derived S 85 (average correlation coefficient = 0.70). Although more directly linked to surface precipitation, polarization indices have been found to be less correlated with radar data, due to limitations inherent in the remote sensing of precipitation at higher latitudes. A stratification of the dataset into frontal and convective events revealed significant variations in these relationships for different types of precipitation events, thus reflecting different cloud microphysical processes associated with precipitation initialization. The relationship between S 85 and radar rain estimates at higher altitudes varies considerably for different convective and frontal events. The sensitivity of S 85 to radar-derived rain rate ranges from 3.1 K mm m 1 h m 1 for a strong convective event to about 25 K mm m 1 h m 1 for the frontal and about 70 mm m 1 h m 1 for the small-scale convective events. For extrapolated surface precipitation estimates, sensitivities decrease to 14 mm m 1 h m 1 and 25 mm m 1 h m 1 for frontal and small-scale convective precipitation, respectively.     

An evaluation of MODIS and SeaWiFS bio-optical algorithms in the Baltic Sea

An extensive bio-optical data set from field measurements was used to evaluate the performance of standard Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color (in-water) algorithms in the Baltic Sea, which represents an example of optically complex Case 2 waters with high concentration of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities, chlorophyll a concentration (Chl a), and absorption coefficient of CDOM, which were taken on 25 cruises between 1993 and 2001. The data cover a wide range of variability with Chl a in surface waters from about 0.3 to 100 mg m⁻³. All the MODIS pigment algorithms examined as well as the SeaWiFS OC4v4 algorithm showed a systematic and large overestimation in chlorophyll retrievals. The mean systematic and random errors based on our entire data set exceeded 150% or even 200% in some cases, making these standard algorithms inadequate for pigment determinations in the Baltic. Although new parameterization of the standard pigment algorithms based on our field measurements in the Baltic resulted in a significant reduction of errors, the overall performance of such regionally tuned algorithms remained unsatisfactory. For example, the mean normalized bias (MNB) for the regionally tuned MODIS chlor_a_2 algorithm was reduced to 26% (from over 200% for the standard algorithm), but the root mean square (RMS) error was still large (>100%). The MODIS K_490 algorithm for estimating the diffuse attenuation coefficient of downwelling irradiance showed the best performance among all the algorithms examined. With the new coefficients based on our field data, the regional version of this algorithm showed an acceptable level of errors, MNB=4% and RMS=30%. In addition to the apparent problems of the standard in-water bio-optical algorithms, we found that the atmospheric correction currently in use for MODIS and SeaWiFS imagery usually fails to retrieve upwelling radiances emerging from the Baltic Sea. The match-up comparisons of the coincident in situ and satellite determinations of normalized water-leaving radiances showed generally poor agreement, especially in the blue spectral region. It appears that new approaches for ocean color algorithms are required in the Baltic Sea.     

ASTLE CIPHER SOLVED

Abstract

This article describes the operation of a small U.S. Navy station in post-World War II China that primarily intercepted Soviet naval traffic as part of the worldwide BOURBON project targeting all Soviet communications systems.     

Sea state in the Baltic Sea from space-borne high-resolution synthetic aperture radar imagery

In this work, remote sensing synthetic aperture radar (SAR) data from X-band TerraSAR-X and TanDEM-X (TS-X and TD-X) satellites have been used to adopt the algorithms for estimating sea state parameters in the specific condition of the Baltic Sea with archipelago islands and where short steep sea state dominates. Since the moving targets can be defocused and shifted in SAR images, sea state consisting of short windsea waves with strong local orbital velocities and wave breaking needs additional effort for accurate estimation of the total significant wave height that consists of swell and windsea parts. The XWAVE_C algorithm, developed for the North Sea, where the long swell waves coming from the Atlantic Ocean are present during storms, was further enhanced for the short steep windsea which dominates under ordinary storm conditions in the Baltics. For the empirical XWAVE_C model function, based on the spectral analysis of subscenes as well as on local wind information, an additional term was incorporated for assessment the minimal windsea significant wave height by applying JONSWAP wave spectra. A term to compensate spectral distortions triggered by windsea waves moving in SAR flight direction has also been introduced. In total, 95 TS-X/TD-X StripMap scenes between 2012 and 2017 were acquired in Eastern Baltic Sea, processed and analysed. The wave height results from SAR images were compared with collocated in situ data from 11 available buoys. The analysed data include both high and low windsea conditions. The comparison of SAR-derived wave heights with measured wave heights shows high agreement with a correlation coefficient r of 0.88. The wind speed, estimated from SAR images, was compared to measurements from 14 collocated in situ stations, yielding a high agreement with an r value of 0.90. This article is focused on the algorithm developments; however, it is also the first study of sea state retrieval in the Baltic Sea using high-resolution satellite-based techniques. The results show the local variability in the wave fields connected to atmospheric features. The observed local wave height can increase by 1–2 m in kilometre-size cells that are accompanied by wind gusts. The developed algorithms are installed in the German Aerospace Center’s (DLR) ground station Neustrelitz and can also be used in near-real-time.     

Spectral optical and bio‐optical relationships in the Oslo Fjord compared with similar results from the Baltic Sea

The spectral shape of the attenuation coefficient c in Baltic waters along the Swedish coast is almost identical to the one in the Oslo Fjord, and there are also strong similarities between these two areas for the absorption coefficient a and the scattering coefficient b as functions of c. However, while the single‐scattering albedo b/c in the Oslo Fjord on an average is 62% and 78% at 425 and 525?nm, respectively, the corresponding numbers for the Gulf of Gdansk are 54% and 61%. Another characteristic difference is that particle absorption plays a much more significant role in the Gulf of Gdansk than in the Oslo Fjord. Thus some parts of the Baltic exhibit similarities with the Oslo Fjord while others display differences, and it cannot be assumed a priori that algorithms from one area will have a general validity in the other.

Algorithms for chlorophyll‐a and yellow substance as functions of colour indices, determined for the southern part of the Baltic Sea between the Pommerian Bight and the Gulf of Gdansk, are clearly not valid for the Oslo Fjord, but the result improves by changing their constants by a best‐fit procedure. We conclude that statistical algorithms for remote sensing are not generally interchangeable between the Baltic and the Oslo Fjord, and that the constants of the algorithms have to be locally tuned.