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Jurnal Geografi
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  This is an Open Access Journal Open Access journal
ISSN (Print) 2549-3078 - ISSN (Online) 2549-3094
Published by Universitas Negeri Semarang Homepage  [79 journals]
  • Uji Ketelitian Data GNSS dengan Metode NTRIP terhadap Variasi Multipath di
           Lingkungan Universitas Negeri Semarang

    • Authors: Fajar Dian Mukti, Fahrudin Hanafi
      First page: 46
      Abstract: Pengukuran menggunakan GNSS sudah mulai dikembangkan di Indonesia. Multipath berpengaruh kepada hasil data yang dihasilkan dari pantulan sinyal dari satelit ke antena GNSS akan terganggu akibat adanya variasi multipath. Penelitian ini bertujuan untuk (1) Mengetahui kualitas data horizontal GNSS dengan kondisi multipath dikawasan UNNES. (2) Mengetahui tingkat ketelitian pengukuran GNSS metode NTRIP terhadap pengukuran terestris metode poligon terbuka terkoreksi sempurna dengan total station. Populasi keadaan variasi multipath meliputi bangunan dan vegetasi di lingkungan kampus UNNES. Sampel yang akan digunakan 37 titik (STA) Control Point dan 2 Benchmark. Pada hasil penelitian diketahui (1) Kualitas data dengan status fixed dapat diperoleh jika masking area yang digunakan 0º - 10º dengan variasi multipath rerata 47,91% untuk vegetasi, 25% untuk bangunan, dan 27,08% area terbuka. Dan data berstatus float dengan variasi multipath rerata 37,80% untuk vegetasi, 37,80% untuk bangunan, dan 24,40% area terbuka. (2) Ketelitian yang dihasilkan yaitu cukup bagus untuk metode fixed dan float, Regresi linier yang dihasilkan status autonomous membuat persebaran data koordinat X menjadi tidak normal dan koordinat Y menyebar normal. Saran dari penelitian ini adalah untuk mengontrol kualitas data dari hasil pengukuran GNSS metode NTRIP dapat dikombinasikan dengan hasil dari pengukuran Total Station metode poligon tertutup.  Dan penelitian selanjutnya dapat menggunakan kombinasi antara jaring kontrol horizontal dan jaring kontrol vertikal untuk mengetahui ketinggian dan kontur yang lebih akurat.Measurement using GNSS has begun to be developed in Indonesia. Multipath affects the results of data generated from the reflection of signals from satellites to GNSS antennas will be disturbed due to multipath variations. This study aims to (1) Determine the quality of GNSS horizontal data with multipath conditions in the UNNES area. (2) Knowing the level of accuracy of the NTRIP method GNSS measurement against the terrestrial measurement of the open polygon method is perfectly corrected by the total station. The population of multipath variations includes buildings and vegetation in the UNNES campus environment. The sample to be used is 37 (STA) Control Point and 2 Benchmarks. In the results of the study, it is known that (1) The quality of data with fixed status can be obtained if the masking area used is 0º - 10º with an average multipath variation of 47.91% for vegetation, 25% for buildings, and 27.08% for open areas. And the data is float status with an average multipath variation of 37.80% for vegetation, 37.80% for buildings, and 24.40% for open areas. (2) The resulting precision is good enough for fixed and float methods, The linear regression generated by the autonomous state makes the distribution of X coordinate data abnormal and the Y coordinate spreads normally. Suggestions regarding of the results from this study is to control the data quality of the GNSS measurement results of the NTRIP method can be combined with the results of the Total Station measurement of the closed polygon method.  And subsequent research can use the combination of horizontal control net and vertical control net to find out the height and contour more accurately.
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.39094
      Issue No: Vol. 19, No. 2 (2022)
       
  • Kajian Karakteristik Aliran Sungai Serang di AWLR Bendungan Kulonprogo
           Berdasarkan Pemodelan Hidrologi HEC-HMS

    • Authors: Si’ta Romadhoniastri, Nur Ayumi, Fahima Ulumia, Nur Azkiyatuz Zahro, Rezis Rahayuli, Rizky Wahyudi, Dimas Maula Hayat, Mohammad Pramono Hadi
      First page: 54
      Abstract: HEC HMS merupakan salah satu aplikasi pemodelan yang dapat digunakan untuk memodelkan nilai limpasan harian maupun bulanan berdasarkan karakteristik DAS. Tujuan penelitian ini adalah 1) Mengkaji karakteristik fisik DAS Serang yang direpresentasikan oleh nilai curve number (CN) 2) Mengkaji karakteristik aliran yang berupa debit puncak, volume outflow, dan waktu puncak dari hidrograf banjir terukur dengan hasil pemodelan menggunakan  HEC-HMS. Nilai CN ditentukan menggunakan metode SCS-CN. Analisis hidrograf banjir dilakukan menggunakan HEC-HMS meliputi perhitungan presipitasi menggunakan gage weight, volume runoff menggunakan SCS CN, direct runoff menggunakan SCS-UH, dan baseflow menggunakan constant monthly. Hasil penelitian menunjukkan CN pada tahun 2019 memiliki nilai 83 pada kondisi AMC I. Hasil kalibrasi menunjukkan nilai objective function dengan metode Peak-Weighted RMS Error cukup baik yaitu sebesar 2.2% dengan selisih antara debit puncak simulasi dan observasi yang nilainya masing-masing adalah 21.2 m3/s dan 21.6 m3/s. Secara keseluruhan, hasil uji statistik validasi diketahui bahwa model HEC-HMS menghasilkan hidrograf model yang sangat baik dilihat dari nilai NSE, R2 dan PBIAS.HEC HMS is a modeling application that can be used to model daily and monthly runoff values based on watershed characteristics. The objectives of this study are 1) to examine the physical characteristics of the Serang watershed which is represented by the curve number (CN) 2) to examine the flow characteristics in the form of peak discharge, outflow volume, and peak time of the flood hydrograph measured by modeling results using HEC-HMS. The CN value is determined using the SCS-CN method. Flood hydrograph analysis was performed using HEC-HMS including calculation of precipitation using gage weight, volume runoff using SCS CN, direct runoff using SCS-UH, and baseflow using constant monthly. The results showed that CN in 2019 had a value of 83 under AMC I conditions. The calibration results showed that the objective function value with the Peak-Weighted RMS Error method was quite good, namely 2.2% with the difference between the simulation peak discharge and the observation, each of which was 21.2 m3. /s and 21.6 m3/s. Overall, the results of the statistical validation test show that the HEC-HMS model produces a very good hydrograph model seen from the NSE, R2 and PBIAS values.
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.33671
      Issue No: Vol. 19, No. 2 (2022)
       
  • Zonasi Bencana Abrasi Pantai Sappoang Kabupaten Polewali Mandar

    • Authors: Hamsah Hamsah, Nirmawala Nirmawala
      First page: 62
      Abstract: This research uses a formula approach. In formula has several variables. The variables in this research are tidal, ocean current speed and direction, wave height and wave period, type of geological structure of the coast and sediment grain size materials, the slope of the beach and coastline direction, wind speed and direction. The number of samples or observation points at 27, with interval distance every point is 200 m. The results of the research were analyzed in the waves of the type formula and determinants of abrasion and sedimentation. Sappoang Beach is one of the marine landforms are more specifically known as a land form bar (deposition of sand along the coast). Conditions beach located around the mouth of the river to the beach physical differences that are in the basin area (central coast), where the force of the waves, and the flow velocity at the beach slope basin area beaches have greater value when compared to the coastal areas near the mouth river. The results showed that there are three conditions in Sappoang Beach beaches of different areas of research currently conducted (the west wind), like sedimentation area, balanced and abraded. Abraded zone and sedimentation zone is more dominant than the beaches that are stable. This is more significant because at the time of measurement, the wind is blowing west wind, given the quantity of variables measuring the higher the coast, so the coastal zone is increasing abraded.
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.34486
      Issue No: Vol. 19, No. 2 (2022)
       
  • Pemetaan Daerah Rawan Banjir di Kota Ambon Menggunakan Sistim Informasi
           Geografis

    • Authors: Heinrich Rakuasa, Joseba Kristina Helwend, Daniel Anthoni Sihasale
      First page: 73
      Abstract: Bencana banjir terjadi hampir setiap tahun di Kota Ambon dan mengingat besarnya dampak dan jumlah korban yang dapat ditimbulkan maka pemetaan daerah rawan banjir merupakan dasar untuk memberikan informasi tentang strategi mitigasi risiko banjir. Penelitian ini bertujuan untuk menganalisis kawasan rawan banjir dan juga memprediksi kawasan permukiman yang berada di kawasan rawan banjir di Kota Ambon. Penelitian ini menggunakan metode Multicriteria Evaluation (MCE) bagi pengambil keputusan dalam menentukan bobot dan metode yang sesuai serta menggunakan Weighted Linear Combination (WLC) dalam menganalisis daerah rawan banjir. Hasil penelitian menunjukkan bahwa Kecamatan Teluk Ambon memiliki wilayah terluas pada setiap kelas kerawanan banjir di Kota Ambon dibandingkan dengan kecamatan lainnya, hal ini dikarenakan kecamatan tersebut merupakan yang terbesar di Kota Ambon. Sedangkan luas lahan pemukiman yang tersebar pada kawasan kelas kerawanan tinggi memiliki persentase luas paling besar yaitu 2.222,06 ha. Sebaran permukiman pada kelas kerawanan sedang seluas 2.214,67 ha yang tersebar di lima kecamatan di Kota Ambon. Sedangkan kawasan terbangun yang berada pada tingkat kerawanan sedang adalah 0,39 ha. Salah satu bentuk antisipasi dan mitigasi bencana banjir adalah dengan memperkirakan seberapa luas lahan terbangun pada kawasan rawan banjir untuk meminimalkan kerugian, baik korban jiwa maupun kerusakan fisik
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.34240
      Issue No: Vol. 19, No. 2 (2022)
       
  • Analisis Peristiwa Angin Kencang dengan Citra Satelit Himawari-8 (Studi
           Kasus: Bangkalan, 17 Oktober 2021)

    • Authors: Fikri Asfahanif, Sayful Amri
      First page: 83
      Abstract: Angin kencang di atas 25 knots dapat menyebabkan kerusakan, misalnya infrastruktur dan tumbangnya pohon. Tujuan penelitian ini untuk mengetahui dinamika atmosfer saat kejadian angin kencang di wilayah Bangkalan, Madura tanggal 17 Oktober 2021. Metode yang digunakan adalah analisis deskriptif terhadap variabel cuaca dan citra satelit Himawari-8 menggunakan aplikasi Sataid. Hasil dari penelitian ini menunjukan terjadinya pembentukan awan-awan konvektif di atas Pulau Madura bagian Timur yang bergerak menuju wilayah Bangkalan di Pulau Madura bagian Barat dengan suhu puncak awan mencapai -58 oC. Pada tanggal 17 Oktober 2021, wilayah Madura berada dalam periode transisi, terlihat dari angin dominannya masih dipengaruhi oleh monsun Australia dan mulai menguatnya monsun Asia. Hal ini memicu terbentuknya shearline di wilayah Madura dan sekitarnya. Selain itu, suhu permukaan laut di sekitar wilayah Madura cukup panas, sehingga meningkatkan penguapan dan memicu labilitas udara yang kuat. Kondisi ini memicu terbentuknya awan konvektif yang menyebabkan terjadinya angin kencang di wilayah tersebut.Strong winds above 25 knots can cause damage, for example, infrastructure and fallen trees. This study aims to determine the dynamics of the atmosphere during strong winds in the Bangkalan, Madura October 17, 2021. The method used was a descriptive analysis of weather variables and satellite imagery of Himawari-8 using the Sataid application. The results indicate the formation of convective clouds over the eastern part of Madura that moves towards the Bangkalan area on the western part of Madura, cloud peak temperatures reaching -58oC. On October 17, 2021, the Madura region is in a transition period, as can be seen from the dominant winds that are still influenced by the Australian monsoon also the Asian monsoon is starting to strengthen. The monsoon triggers the formation of a shearline in Madura and surrounding areas. Furthermore, the sea surface temperature around the Madura area is quite hot, thereby increasing evaporation and triggering strong air lability. This condition triggers the formation of convective clouds that cause strong winds.
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.34826
      Issue No: Vol. 19, No. 2 (2022)
       
  • Analysis of Rice Field Drought Level in Pemalang Regency 2019 – 2021

    • Authors: Indah Purwati, Arie Yulfa
      First page: 92
      Abstract: Pemalang is a district that has rice fields up to 36 thousand hectares and becomes a buffer area for rice commodity in Central Java and becomes a focus in maintaining availability and food reserves. However, Pemalang Regency is vulnerable to the threat of drought that often hits the Central Java region. Therefore, information is needed about rice field drought as a form of mitigation and supporting food security by the sustainable development goals (SDGs). The purpose of this research is to determine the level of rice fields' drought in the rainy and dry seasons from 2019 to 2021 and displays in the form of web gis that all circles can access. The data needed in this study include normalized difference vegetation index (NDVI) map, normalized difference water index (NDWI) map, land surface temperature (LST) map, hydrogeology map, land type map, and rice field map. The result of this study is the formation of a map of the drought level of rice fields in the Pemalang Regency divided into five classes, namely very low, low, medium, high, and very high. Ulujami and Belik are the sub-districts with the broadest moderate drought rate from the data processing. Then Ulujami, Watukumpul, and Belik are districts with the broadest area of high drought, and Randudongkal is a subdistrict with the broadest very high drought area.
      PubDate: 2022-07-01
      DOI: 10.15294/jg.v19i2.35290
      Issue No: Vol. 19, No. 2 (2022)
       
 
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